Magnetic susceptibility, magnetization, magnetic moment and

Transcription

Symmetry 2015, xx, 1-x; doi:10.3390/——
OPEN ACCESS
symmetry
ISSN 2073-8994
www.mdpi.com/journal/symmetry
Article
Supersymmetry with radiatively-driven naturalness:
implications for WIMP and axion searches
arXiv:1503.04137v1 [hep-ph] 13 Mar 2015
Kyu Jung Bae1 , Howard Baer1, *, Vernon Barger2 , Michael R. Savoy1 and Hasan Serce1
1
2
Dept. of Physics and Astronomy, University of Oklahoma, Norman, OK 73019, USA
Dept. of Physics, University of Wisconsin, Madison, WI 53706, USA
* Author to whom correspondence should be addressed; baer@nhn.ou.edu, 405-325-3961 ext 36315
Received: xx / Accepted: xx / Published: xx
Abstract: By insisting on naturalness in both the electroweak and QCD sectors of the
MSSM, the portrait for dark matter production is seriously modified from the usual WIMP
miracle picture. In SUSY models with radiatively-driven naturalness (radiative natural
SUSY or RNS) which include a DFSZ-like solution to the strong CP and SUSY µ problems,
dark matter is expected to be an admixture of both axions and higgsino-like WIMPs.
The WIMP/axion abundance calculation requires simultaneous solution of a set of coupled
Boltzmann equations which describe quasi-stable axinos and saxions. In most of parameter
space, axions make up the dominant contribution of dark matter although regions of WIMP
dominance also occur. We show the allowed range of PQ scale fa and compare to the values
expected to be probed by the ADMX axion detector in the near future. We also show WIMP
detection rates which are suppressed from usual expectations because now WIMPs comprise
only a fraction of the total dark matter. Nonetheless, ton-scale noble liquid detectors should
be able to probe the entirety of RNS parameter space. Indirect WIMP detection rates are less
propitious since they are reduced by the square of the depleted WIMP abundance.
Keywords: supersymmetry; dark matter; WIMPs; axions; naturalness
arXiv:1503.04109v1 [hep-ph] 13 Mar 2015
Prepared for submission to JCAP
Dark matter signals at neutrino
telescopes in effective theories
Riccardo Catenaa
a Institut
f¨
ur Theoretische Physik, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
E-mail: riccardo.catena@theorie.physik.uni-goettingen.de
Abstract. We constrain the effective theory of one-body dark matter-nucleon interactions
using neutrino telescope observations. We derive exclusion limits on the 28 coupling constants
of the theory, exploring interaction operators previously considered in dark matter direct
detection only, and using new nuclear response functions recently derived through nuclear
structure calculations. We determine for what interactions neutrino telescopes are superior
to current direct detection experiments, and show that Hydrogen is not the most important
element in the exclusion limit calculation for the majority of the spin-dependent operators.
Keywords: dark matter theory, dark matter experiments
RUP-15-5
RESCEU-4/15
Cosmological long-wavelength solutions and primordial black hole formation
1
Tomohiro Harada,∗ 2 Chul-Moon Yoo,† 3 Tomohiro Nakama,‡ and 1 Yasutaka Koga§
1
Department of Physics, Rikkyo University, Toshima, Tokyo 171-8501, Japan
Gravity and Particle Cosmology Group, Division of Particle and Astrophysical Science,
Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan and
3
Research Center for the Early Universe (RESCEU), Graduate School of Science,
University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
(Dated: March 16, 2015)
2
arXiv:1503.03934v1 [gr-qc] 13 Mar 2015
We construct cosmological long-wavelength solutions without symmetry in general gauge conditions which are compatible with the long-wavelength scheme. We then specify the relationship
among the solutions in different time slicings. Nonspherical long-wavelength solutions are particularly important for primordial structure formation in the epoch of very soft equations of state.
Applying this general framework to spherical symmetry, we show the equivalence between longwavelength solutions in the constant mean curvature slicing with conformally flat spatial coordinates
and asymptotic quasi-homogeneous solutions in the comoving slicing with the comoving threading.
We derive the correspondence relation between these two solutions and compare the results of numerical simulations of primordial black hole (PBH) formation in these two different approaches.
To discuss the PBH formation, it is convenient and conventional to use δ˜c , the value which the
averaged density perturbation at threshold in the comoving slicing would take at horizon entry in
the first-order long-wavelength expansion. We numerically find that within (approximately) compensated models, the sharper the transition from the overdense region to the FRW universe is, the
larger the δ˜c becomes. We suggest that, for the equation of state
√ p = (Γ − 1)ρ,
we can apply the
analytic formula for the minimum δ˜c,min ≃ 3Γ/(3Γ + 2) sin2 π Γ − 1/(3Γ − 2) and the maximum
δ˜c,max ≃ 3Γ/(3Γ + 2). As for the threshold peak value of the curvature perturbation ψ0,c , we find
that the sharper the transition is, the smaller the ψ0,c becomes. We analytically explain this intriguing feature qualitatively with a compensated top-hat density model. We also analytically deduce
an environmental effect for primordial structure formation in the presence of much longer wavelength perturbations using simplified models. We conclude that PBH formation can be significantly
suppressed (enhanced) in the underlying positive (negative) density perturbation of much longer
wavelength, provided that the smaller value of ψ0,c implies higher production rate of PBHs.
PACS numbers: 04.70.Bw, 98.80.-k, 97.60.Lf
∗
†
‡
§
harada@rikkyo.ac.jp
yoo@gravity.phys.nagoya-u.ac.jp
nakama@resceu.s.u-tokyo.ac.jp
koga@rikkyo.ac.jp
Numerical solution of the non-linear Schr¨
odinger equation using smoothed-particle
hydrodynamics
Philip Mocz∗
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
arXiv:1503.03869v1 [physics.comp-ph] 12 Mar 2015
Sauro Succi†
Istituto per le Applicazioni del Calcolo, CNR, Viale del Policlinico 137, I-00161, Roma, Italy
Institute of Applied Computational Science, Harvard School of Engineering and Applied Sciences,
Northwest B162, 52 Oxford Street, Cambridge, MA 02138, USA
We formulate a smoothed-particle hydrodynamics numerical method, traditionally used for the
Euler equations for fluid dynamics in the context of astrophysical simulations, to solve the non-linear
Schr¨
odinger equation in the Madelung formulation. The probability density of the wavefunction is
discretized into moving particles, whose properties are smoothed by a kernel function. The traditional fluid pressure is replaced by a quantum pressure tensor, for which a novel, robust discretization
is found. We demonstrate our numerical method on a variety of numerical test problems involving
the simple harmonic oscillator, Bose-Einstein condensates, collapsing singularities, and dark matter
halos governed by the Gross-Pitaevskii-Poisson equation. Our method is conservative, applicable to
unbounded domains, and is automatically adaptive in its resolution, making it well suited to study
problems with collapsing solutions.
PACS numbers: 02.60.-x, 03.65.-w, 47.11.-j, 67.85.Hj, 67.85.Jk
I.
INTRODUCTION
Quantum mechanics is one of the basic pillars of modern physics. The Schrödinger equation describes the
quantum mechanical evolution of the wavefunction of a
particle over time. The non-linear Schrödinger equation
(NLSE), also called the Gross-Pitaevskii equation, is a
non-linear extension of the Schrödinger equation, which
describes the ground state of a quantum system of identical bosons using a single-particle wavefunction approximation and a pseudopotential model for interaction. It
is ideal for describing a Bose-Einstein condensate (BEC):
dilute gas of bosons in a low-temperature state very close
to absolute zero. BECs were first predicted in the early
days of quantum theory by Bose and Einstein in 19241925. The first realization in the laboratory was achieved
in 1995 [1, 2], which marked a new era in atomic, molecular and optical (AMO) physics and quantum optics [3].
The NLSE has applications and extensions to entirely
different physical systems as well, including the propagation of light in non-linear fiber optics [4], Langmuir waves
in plasmas [5], and self-gravitating BEC models for dark
matter, governed by the Gross-Pitaevskii-Poisson equations [6].
The NLSE is challenging to solve and almost always
requires numerical solutions. Ongoing research has led
to the development of a variety of methods to solve these
systems in various contexts, such as those for solving
time-evolution of BEC systems [3, 7–10] and obtaining
their ground states [11–14]. These methods solve for the
∗
†
pmocz@cfa.harvard.edu
succi@iac.cnr.it
solution to the NSLE in the standard form, and typically employ finite-difference, finite-element, or spectral
methods. Other non-standard methods for solving quantum systems have been proposed as well, such as lattice
Boltzmann [15, 16]. Each method has different strengths
and limitations when applied to different systems [17].
We propose a novel, conservative numerical approach
for solving the NLSE that is quite different from the standard approaches. We solve the NLSE in Madelung hydrodynamic form, using a smoothed particle hydrodynamics (SPH) algorithm. The Schrödinger equation, as well
as the NLSE, can be reformulated under the Madelung
transformation to take a different form that resembles the
fluid equations [18]. The equation in Madelung form describes the evolution of the quantum probability density
of the wavefunction under a quantum “pressure” tensor,
and is equivalent to the standard form.
SPH is a particle-based method for computational fluid
dynamics. It was originally invented to simulate polytropic stellar models under non-axisymmetric conditions
[19, 20]. It has since been extended and coupled with
additional physical processes and plays a central role
in astrophysical and cosmological simulations [21–23].
SPH operates independently of any grid, unlike finitedifference, finite-volume, or finite-element methods, and
interactions between volume elements, such as the pressure gradient, are represented as a force between particles. The method is purely Lagrangian, meaning that
interactions and derivatives are evaluated in a coordinate
system attached to a moving fluid element. The two fundamental ideas of SPH are (1) to evolve the positions
and velocities of particles according to the calculation of
the forces on each particle at each time-step, and (2) to
use an interpolating/smoothing kernel to calculate forces
arXiv:1503.03214v1 [gr-qc] 11 Mar 2015
Non-minimally coupled varying
constants quantum cosmologies
Adam Balcerzaka,b
a Institute
of Physics, University of Szczecin,
Wielkopolska 15, 70-451 Szczecin, Poland
b Copernicus Center for Interdisciplinary Studies,
Sławkowska 17, 31-016 Kraków, Poland
E-mail: abalcerz@wmf.univ.szczecin.pl
Abstract. We consider gravity theory with varying speed of light and varying gravitational
constant. Both constants are represented by non-minimally coupled scalar fields. We examine the cosmological evolution in the near curvature singularity regime. We find that at
the curvature singularity the speed of light goes to infinity while the gravitational constant
vanishes. This corresponds to the Newton’s Mechanics limit represented by one of the vertex
of the Bronshtein-Zelmanov-Okun cube [1, 2]. The cosmological evolution includes both the
pre-big-bang and post-big-bang phases separated by the curvature singularity. We also investigate the quantum counterpart of the considered theory and find the probability of transition
of the universe from the collapsing pre-big-bang phase to the expanding post-big-bang phase.
Mon. Not. R. Astron. Soc. 000, 000–000 (0000)
Printed 16 March 2015
(MN LATEX style file v2.2)
arXiv:1503.04195v1 [astro-ph.GA] 13 Mar 2015
Photoionization analysis of chemo-dynamical dwarf galaxies
simulations
B.
Melekh1 , S. Recchi2 , G. Hensler2, O. Buhajenko1,
1
2
Department of Astrophysics, Ivan Franko National University, Kyrylo & Methodiy str. 8, 79005 Lviv, Ukraine
Institute for Astrophysics, University of Vienna, Türkenschanzstrasse 17, A-1180 Vienna, Austria
Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal, 12 March 2015.
ABSTRACT
Photoionization modelling allows to follow the transport, the emergence, and the absorption of
photons taking into account all important processes in nebular plasmas. Such modelling needs
the spatial distribution of density, chemical abundances and temperature, that can be provided
by chemo-dynamical simulations (ChDS) of dwarf galaxies. We perform multicomponent
photoionization modelling (MPhM) of the ionized gas using 2-D ChDSs of dwarf galaxies.
We calculate emissivity maps for important nebular emission lines. Their intensities are used
to derive the chemical abundance of oxygen by the so-called T e − and R23 −methods. Some
disagreements are found between oxygen abundances calculated with these methods and the
ones coming from the ChDSs. We investigate the fraction of ionizing radiation emitted in the
star-forming region which is able to leak out the galaxy. The time- and direction-averaged
escape fraction in our simulation is 0.35–0.4. Finally, we have calculated the total Hα luminosity of our model galaxy using Kennicutt’s calibration to derive the star-formation rate. This
value has been compared to the ’true’ rate in the ChDSs. The Hα -based star-formation rate
agrees with the true one only at the beginning of the simulation. Minor deviations arise later
on and are due in part to the production of high-energy photons in the warm-hot gas, in part
to the leakage of energetic photons out of the galaxy. The effect of artificially introduced thin
dense shells (with thicknesses smaller than the ChDSs spatial resolution) is investigated, as
well.
Key words: Galaxies: modelling – Galaxies: dwarf – Galaxies: evolution – Galaxies: ISM –
Galaxies: emission lines
1 INTRODUCTION
The main information about physical processes and the physical
state of the interstellar medium (ISM) in star-forming dwarf galaxies (DGs) are obtained from observed emission line spectra from
their nebular components – gaseous nebulae or nebulae surrounding the compact star-forming (SF) region (see the textbooks of
Dopita & Sutherland 2003; Osterbrock & Ferland 2005).
Line intensity ratios are used to infer the physical state (density, temperature, chemical composition) of ionized regions. These
indicators are commonly dubbed diagnostic methods and their use
date back to the seventies (Searle 1971; Pagel et al. 1979), although research is still ongoing in this field (see Pilyugin 2003;
Pettini & Pagel 2004; Stasińska 2006). As it is well known, (see
e.g. Osterbrock & Ferland 2005) some intensity ratios (such as
[OIII]λ4363Å versus λ4959Å and λ5007Å) in range typical for
HII regions are much more sensitive to the electron temperature
than to electron density, whereas others (e.g. [SII]λ6716Å/λ6731Å
and [OII]λ3729Å/λ3726Å) are sensitive to the electron density. In
some cases, intensity ratios are very sensitive to both T e and ne . In
this case, two or more diagnostics must be used at the same time to
determine both quantities (see Golovaty et al. 1993; Shaw 1995).
Physical conditions inside nebulae can thus be recovered and, from
them, the relative abundances of ions can be determined.
Most of diagnostic methods assume constant electron temperatures and densities as well as ionic abundances over the whole
ionized regime, although many attempts can be found in the literature to relax this hypothesis. The assumption of non-uniformity is
necessary for instance to explain the discrepancies between electron temperatures found with different diagnostic methods. In particular, the temperature fluctuations are characterized by the socalled t2 parameter (Peimbert 1967). A different approach was
proposed by Mathis et al. (1998), who used ratios f between
weights of emitting regions1 to characterize the temperature inhomogeneities. Based on this work, Stasińska (2002) modified the
Peimbert’s t2 parameter to allow for temperature inhomogeneities
in ionized nebulae. However, in all these methods (and in other
1 f = (N n V )/(N n V ), where n and n are electron densities in emit2 2 2
1 1 1
1
2
ting regions, V1 and V2 are their volumes, and N1 , N2 are densities of the
emitting ions
Library and Information Services in Astronomy VII
ASP Conference Series, Vol. TBD
Andras Holl, Soizick Lesteven, Dianne Dietrich, and Antonella Gasperini, eds.
c 2014 Astronomical Society of the Pacific
arXiv:1503.04194v1 [astro-ph.IM] 13 Mar 2015
ADS: The Next Generation Search Platform
Alberto Accomazzi, Michael J. Kurtz, Edwin A. Henneken, Roman Chyla,
James Luker, Carolyn S. Grant, Donna M. Thompson, Alexandra Holachek,
Rahul Dave, Stephen S. Murray
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge,
MA 02138, USA
Abstract. Four years after the last LISA meeting, the NASA Astrophysics Data System (ADS) finds itself in the middle of major changes to the infrastructure and contents
of its database. In this paper we highlight a number of features of great importance
to librarians and discuss the additional functionality that we are currently developing.
Starting in 2011, the ADS started to systematically collect, parse and index full-text
documents for all the major publications in Physics and Astronomy as well as many
smaller Astronomy journals and arXiv e-prints, for a total of over 3.5 million papers.
Our citation coverage has doubled since 2010 and now consists of over 70 million
citations. We are normalizing the affiliation information in our records and, in collaboration with the CfA library and NASA, we have started collecting and linking funding
sources with papers in our system. At the same time, we are undergoing major technology changes in the ADS platform which affect all aspects of the system and its
operations. We have rolled out and are now enhancing a new high-performance search
engine capable of performing full-text as well as metadata searches using an intuitive
query language which supports fielded, unfielded and functional searches. We are currently able to index acknowledgments, affiliations, citations, funding sources, and to
the extent that these metadata are available to us they are now searchable under our
new platform. The ADS private library system is being enhanced to support reading
groups, collaborative editing of lists of papers, tagging, and a variety of privacy settings when managing one’s paper collection. While this effort is still ongoing, some
of its benefits are already available through the ADS Labs user interface and API at
http://adslabs.org/adsabs/.
1.
Introduction
The ADS was originally conceived over 20 years ago as a system to support the discovery and retrieval of data from the NASA Astrophysics missions and the scholarly literature written about it (Kurtz et al. 2000). With the restructuring of the ADS program
in 1994, the system became the primary service providing a bibliographic discovery
platform to researchers in Astronomy, Astrophysics, and related fields. Today, the ADS
is best described as a “disciplinary repository” for bibliographic content in Astronomy
and Physics. In addition to its search capabilities, ADS tracks citations between papers,
links to datasets associated with the publications, provides article-level metrics, and
features personalized notification services to registered users.
Over its lifetime, ADS has seen an astonishing growth in its data holdings and
capabilities. The current number of bibliographic records in ADS is now above 10
1
Mon. Not. R. Astron. Soc. , (2015)
Defining the frame of minimum Hubble expansion variance
arXiv:1503.04192v1 [astro-ph.CO] 13 Mar 2015
James H. McKay⋆ & David L. Wiltshire†
Department of Physics & Astronomy, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand
16 March 2015
ABSTRACT
We characterize a cosmic rest frame in which the variation of the spherically averaged
Hubble expansion is most uniform, under local Lorentz boosts of the central observer.
Using the COMPOSITE sample of 4534 galaxies, we identify a degenerate set of candidate minimum variance frames, which includes the rest frame of the Local Group (LG)
of galaxies, but excludes the standard Cosmic Microwave Background (CMB) frame.
Candidate rest frames defined by a boost from the LG frame close to the plane of the
galaxy have a statistical likelihood similar to the LG frame. This may result from a
lack of constraining data in the Zone of Avoidance in the COMPOSITE sample. We
extend our analysis to the Cosmicflows-2 (CF2) sample of 8,162 galaxies. While the
signature of a systematic boost offset between the CMB and LG frames averages is
still detected, the spherically averaged expansion variance in all rest frames is significantly larger in the CF2 sample than would be reasonably expected. We trace this to
an omission of any correction for inhomogeneous distribution Malmquist bias in the
CF2 distances. Systematic differences in the inclusion of the large SFI++ subsample
into the COMPOSITE and CF2 catalogues are analysed. Our results highlight the
importance of a careful treatment of Malmquist biases for future peculiar velocities
studies, including tests of the hypothesis of Wiltshire et al. (2013) that a significant
fraction of the CMB temperature dipole may be nonkinematic in origin.
Key words: cosmology: observations — cosmology: theory — distance scale
1
INTRODUCTION
Although the Universe is spatially homogeneous in some statistical sense, at the present epoch it exhibits a complex hierarchical structure, with galaxy clusters forming knots, filaments and sheets that thread and surround voids, in a complex cosmic web (Forero–Romero et al. 2009; Bilicki et al.
2014; Einasto 2014). Deviations from homogeneity are conventionally treated in the framework of peculiar velocities,
by which the mean redshift, z, and luminosity distance, r,
of a galaxy cluster are converted to a peculiar velocity according to
vpec = cz − H0 r
(1)
where c is the speed of light and H0
=
100 h km sec−1 Mpc−1 the Hubble constant.
The peculiar velocity framework makes a strong geometrical assumption over and above what is demanded
by general relativity. In particular, the quantity vpec defined by (1) only has the physical characteristics of a velocity if one implicitly assumes the spatial geometry on all
⋆
E-mail: j.mckay14@imperial.ac.uk
† E-mail: david.wiltshire@canterbury.ac.nz
c 2015 RAS
scales larger than those of bound systems is exactly described by a homogeneous isotropic Friedmann-LemaˆıtreRobertson-Walker (FLRW) model with a single cosmic scale
factor, a(t), whose derivative defines a single global Hubble
constant, H0 = a/a|
˙ t0 . Deviations from the uniform expansion are then ascribed to local Lorentz boosts of each galaxy
cluster with respect to the spatial hypersurfaces of average
homogeneity.
It is a consequence of general relativity, however, that
inhomogeneous matter distributions generally give rise to a
differential expansion of space that cannot be reduced to a
single uniform expansion plus local boosts. This is a feature
of general exact solutions to the cosmological Einstein equations, such as the Lemaˆıtre–Tolman–Bondi (LTB) (Lemaˆıtre
1933; Tolman 1934; Bondi 1947) and Szekeres (1975) models.
Any definition of the expansion rate in such models depends
on the spatial scale relative to that of the inhomogeneities.
Although one can define scale dependent Hubble parameters
for specific exact solutions – for example, given the spherical
symmetry of the LTB model – the actual cosmic web is sufficiently complex that in reality one must deal with spatial
or null cone averages in general relativity.
In recent work Wiltshire et al. (2013) examined the
variation of the Hubble expansion from a fresh perspec-
The Chemical Composition of τ Ceti and Possible Effects on Terrestrial
Planets
arXiv:1503.04189v1 [astro-ph.EP] 13 Mar 2015
Michael Pagano1 , Amanda Truitt1 , Patrick A. Young1 , Sang-Heon Shim1
ABSTRACT
τ Ceti (HD10700), a G8 dwarf with mass 0.78 M , is a close (3.65 pc) sun-like
star where 5 possibly terrestrial planet candidates (minimum masses of 2, 3.1, 3.5,
4.3, and 6.7 M⊕ ) have recently been discovered. We report abundances of 23 elements
using spectra from the MIKE spectrograph on Magellan. We find [Fe/H] = −0.49
and T e f f = 5387 K. Using stellar models with the abundances determined here, we
calculate the position of the classical habitable zone with time. At the current best fit
age, 7.63+0.87
−1.5 Gy, up to two planets (e and f) may be in the habitable zone, depending
on atmospheric properties. The Mg/Si ratio of the star is found to be 2.01, which is
much greater than for Earth (∼1.2). With a system that has such an excess of Mg to
Si ratio it is possible that the mineralogical make-up of planets around τ Ceti could
be significantly different from that of Earth, with possible oversaturation of MgO,
resulting in an increase in the content of olivine and ferropericlase compared with
Earth. The increase in MgO would have a drastic impact on the rheology of the mantles
of the planets around τ Ceti.
Subject headings: astrobiology, planets and satellites: composition, planets and satellites: interiors, stars: abundances, stars: individual(τ Ceti.)
1.
Introduction
With the number of extrasolar planets increasing rapidly, it appears that Earth-sized planets
in their host star’s habitable zone (HZ, (e.g. Kasting, Whitmire, & Reynolds 1993; Kopparapu et
al. 2013a)) should be numerous (Marcy et al. 2000; Gaidos 2013; Dressing & Charbonneau 2013;
Kasting et al. 2013; Petigura et al. 2013). In two decades we have progressed from having no
candidate planets to having too many to practically search for detectable biosignatures. A more
nuanced analysis than the location of a planet relative to the instantaneous HZ is necessary to
choose among candidates. One way of conceptualizing this process is through a “detectability
1
School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287
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arXiv:1503.04176v1 [astro-ph.SR] 13 Mar 2015
SGRS AND AXPS AS MASSIVE FAST ROTATING HIGHLY
MAGNETIZED WHITE DWARFS: THE CASE OF SGR 0418+5729
K. BOSHKAYEV1,2,3 , J.A. RUEDA1,2 AND R. RUFFINI1,2
1 Department
of Physics and ICRA, Sapienza University of Rome,
Aldo Moro Square 5, I-00185 Rome, Italy
2 ICRANet, Square of Republic 10, I-65122 Pescara, Italy
3 Physicotechnical Department, Al-Farabi Kazakh National University,
Al-Farabi avenue 71, 050038 Almaty, Kazakhstan;
∗ E-mail: kuantay@icra.it, jorge.rueda@icra.it, ruffini@icra.it
We describe one of the so-called low magnetic field magnetars SGR 0418+5729, as a
massive fast rotating highly magnetized white dwarf following Malheiro et. al.1 We give
bounds for the mass, radius, moment of inertia, and magnetic field for these sources, by
requesting the stability of realistic general relativistic uniformly rotating configurations.
Based on these parameters, we improve the theoretical prediction of the lower limit of
the spin-down rate of SGR 0418+5729. In addition, we compute the electron cyclotron
frequencies corresponding to the predicted surface magnetic fields.
Keywords: general relativistic white dwarfs; SGRs and AXPs; spin-down rate.
1. Introduction
Soft Gamma Ray Repeaters (SGRs) and Anomalous X-ray Pulsars (AXPs) are
a class of compact objects that show interesting observational properties see e.g.
Mereghetti (2008):2 rotational periods in the range P ∼ (2–12) s, a narrow range
with respect to the wide range of ordinary pulsars P ∼ (0.001–10) s; spin-down
rates P˙ ∼ (10−13 –10−10 ), larger than ordinary pulsars P˙ ∼ 10−15 ; strong outburst
of energies ∼ (1041 –1043 ) erg, and for the case of SGRs, giant flares of even large
energies ∼ (1044 –1047 ) erg, not observed in ordinary pulsars.
The observation of SGR 0418+5729 with a rotational period of P = 9.08 s, an
upper limit of the first time derivative of the rotational period P˙ < 6.0 × 10−15
Rea et. al.(2010),12 and an X-ray luminosity of LX = 6.2 × 1031 erg s−1 can be
considered as the Rosetta Stone for alternative models of SGRs and AXPs.
The magnetar model, based on a neutron star of fiducial parameters M =
1.4M⊙, R = 10 km and a moment of inertia I = 1045 g cm2 , needs a magnetic field
larger than the critical field for vacuum polarization Bc = m2e c3 /(e~) = 4.4 × 1013 G
in order to explain the observed X-ray luminosity in terms of the release of magnetic
energy see4,5 for details. The inferred upper limit of the surface magnetic field of
SGR 0418+5729 B < 7.5×1012 G describing it as a neutron star see Rea et. al.12 for
details, is well below the critical field, which has challenged the power mechanism
based on magnetic field decay in the magnetar scenario.
Alternatively, it has been recently pointed out how the pioneering works of
Morini et. al.10 and Paczynski11 on the description of 1E 2259+586 as a white
dwarf (WD) can be indeed extended to all SGRs and AXPs. These WDs were
assumed to have fiducial parameters M = 1.4M⊙, R = 103 km, I = 1049 g cm2 ,
and magnetic fields B & 107 G see1 for details inferred from the observed rotation
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GENERAL RELATIVISTIC AND NEWTONIAN WHITE DWARFS
K. BOSHKAYEV1,2,3 , J.A. RUEDA1,2 , R. RUFFINI1,2 AND I. SIUTSOU2
1 Department
of Physics and ICRA, Sapienza University of Rome,
Aldo Moro Square 5, I-00185 Rome, Italy
2 ICRANet, Square of Republic 10, I-65122 Pescara, Italy
3 Physicotechnical Department, Al-Farabi Kazakh National University,
Al-Farabi avenue 71, 050038 Almaty, Kazakhstan;
∗ E-mail: kuantay@icra.it, jorge.rueda@icra.it, ruffini@icra.it, siutsou@icranet.org
The properties of uniformly rotating white dwarfs (RWDs) are analyzed within the framework of Newton’s gravity and general relativity. In both cases Hartle’s formalism is applied to construct the internal and external solutions to the field equations. The white
dwarf (WD) matter is described by the Chandrasekhar equation of state. The region of
stability of RWDs is constructed taking into account the mass-shedding limit, inverse βdecay instability, and the boundary established by the turning points of constant angular
momentum J sequences which separates stable from secularly unstable configurations.
We found the minimum rotation period ∼ 0.28 s in both cases and maximum rotating
masses ∼ 1.534M⊙ and ∼ 1.516M⊙ for the Newtonian and general relativistic WDs,
respectively. By using the turning point method we show that general relativistic WDs
can indeed be axisymmetrically unstable whereas the Newtonian WDs are stable.
Keywords: Newtonian and general relativistic white dwarfs; maximum mass; minimum
period; stability.
1. Introduction
Recently, equilibrium configurations of non-rotating (static) 4 He, 12 C, 16 O and 56 Fe
white dwarfs (WDs) within general relativity (GR) have been constructed in Ref. 1.
The white dwarf matter has been there described by the relativistic generalization
of the Feynman-Metropolis-Teller (RFMT) equation of state (EOS) obtained by
Rotondo et al.2 A new mass-radius relation that generalizes both the works of
Chandrasekhar3 and Hamada & Salpeter4 has been there obtained, leading to a
smaller maximum mass and a larger minimum radius with respect to the previous
calculations. In addition, it has been shown how both GR and inverse β-decay are
relevant for the determination of the maximum stable mass of non-rotating WDs.
It is therefore of interest to generalize the above results to the case of rotation.
As a first attempt, we constructed in Ref. 5 general relativistic uniformly rotating
WDs in the simplified case when microscopic Coulomb screening is neglected in the
EOS, following the Chandrasekhar3 approximation by describing the matter as a
locally uniform fluid of electrons and nuclei. The average molecular weight in the
Chandrasekhar EOS is µ = A/Z, where A is the mass number and Z is the number
of protons in a nucleus.
As a second attempt, in Ref. 6 we calculated the maximum mass of rotating
4
He, 12 C, 16 O and 56 Fe WDs using the Salpeter11 and the RFMT EOS. As a result
we obtained there different maximum mass for different chemical composition of
WD matter.
As a third attempt, in Ref. 7 we investigated the stability of general relativistic
(MN LaTEX style file v2.2)
arXiv:1503.04170v1 [astro-ph.HE] 13 Mar 2015
Collisionless Shocks and TeV Neutrinos before Supernova
Shock Breakout from an Optically Thick Wind
G. Giacinti1⋆ and A. R. Bell1
1 University
of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom
Released 2014 Xxxxx XX
ABSTRACT
During a supernova explosion, a radiation-dominated shock (RDS) travels through
its progenitor. A collisionless shock (CS) is usually assumed to replace it during
shock breakout (SB). We demonstrate here that for some realistic progenitors enshrouded in optically thick winds, such as possibly SN 2008D, a CS forms deep inside
the wind, soon after the RDS leaves the core, and therefore significantly before SB.
The RDS does not survive the transition from the core to the thick wind when the
wind close to the core is not sufficiently dense to compensate for the r−2 dilution
of photons due to shock curvature. This typically happens when the shock velocity
˙
r∗
w
˙
is . 0.1c ( 10 ukm/s
)( 5·10−4MM⊙ /yr )−1 ( 1013
cm ), where uw , M and r∗ are respectively the
wind velocity, mass-loss rate and radius of the progenitor star. The radiative CS results in a hard spectrum of the photon flash at breakout, which would produce an
X-ray flash. Cosmic ray acceleration would start before SB, for such progenitors. A
fraction of secondary TeV neutrinos can reach the observer up to more than ten hours
before the first photons from breakout, providing information on the invisible layers
of the progenitor.
Key words: acceleration of particles – plasmas – shock waves – cosmic rays – supernovae: general.
1
INTRODUCTION
Type Ib/c and II supernovae (SNe) are generated by core
collapse in massive stars. When the central engine forms, a
shock wave is launched through the hydrostatic core of the
progenitor. The shock is radiation-dominated (or radiationmediated), i.e. the radiation pressure in the downstream
exceeds the fluid pressure (Zel’dovich & Raizer 1966). Once
the radiation-dominated shock (RDS) reaches the optically
thin outer layers of the stellar core or of its wind (if optically thick), photons cannot stay confined in the immediate
downstream and escape ahead of the shock. This flash of
photons corresponds to shock breakout (SB) (Colgate 1974;
Falk 1978; Klein & Chevalier 1978; Chevalier & Klein
1979;
Ensman & Burrows
1992;
Matzner & McKee
1999; Blinnikov et al. 2000; Calzavara & Matzner 2004;
Waxman et al. 2007; Katz et al. 2010, 2012; Piro et al. 2010;
Nakar & Sari 2010; Sapir et al. 2011, 2013). Up until now
a few of them have been observed (Campana et al. 2006;
Gezari et al. 2008; Modjaz et al. 2009; Schawinski et al.
2008; Soderberg et al. 2008; Ofek et al. 2010), and some Xray flashes (XRFs) may be related to SB (e.g. Kulkarni et al.
(1998); Tan et al. (2001); Mazzali et al. (2008); Katz et al.
⋆
E-mail: gwenael.giacinti@physics.ox.ac.uk
(2011)). See Ofek et al. (2013a,b) and Murase et al. (2014)
for radiative signatures at and following breakout.
At SB, the RDS disappears and a collisionless shock (CS) later forms (Chevalier & Klein 1979;
Ensman & Burrows
1992;
Waxman & Loeb
2001;
Chevalier & Fransson 2008). The Larmor radius rL of
suprathermal particles is smaller than the width of the
RDS, which is ≃ λc/3us for a shock velocity us and photon
mean free path λ (Weaver 1976). On the other hand, rL is
larger than the CS width (Bell 1978a,b) and diffusive shock
acceleration becomes possible. A thorough understanding
of the CS formation time is then crucial to study the
onset of CR acceleration, when very high energies might
be reached: & TeV (Waxman & Loeb 2001; Katz et al.
2011), PeV (Tatischeff 2009; Bell et al. 2013), and maybe
ultra-high energies for transrelativistic SNe (Budnik 2008).
Post-main-sequence mass-loss of massive stars is sufficiently high for some SN progenitors, such as some WolfRayet (WR) stars, blue and red supergiants (RSG), to
end up surrounded with optically thick winds (Crowther
2007; Langer 2012). Also, remarkable outbursts can occur before the explosion, see e.g. Ofek et al. (2013b) and
Svirski & Nakar (2014). For optically thick winds, the hydrostatic surface is not observable, which complicates our
understanding of the late stages of massive star evolu-
Astronomy & Astrophysics manuscript no. Version08
March 16, 2015
c
ESO
2015
Letter to the Editor
Candidate hypervelocity stars of spectral type G and K revisited
E. Ziegerer1 , M. Volkert1 , U. Heber1 , A. Irrgang1 , B.T. Gänsicke2 , and S. Geier3,1
1
2
3
Dr. Remeis-Observatory & ECAP, Astronomical Institute, Friedrich-Alexander University Erlangen-Nürnberg, Sternwartstr. 7,
96049 Bamberg, Germany
e-mail: eva.ziegerer@sternwarte.uni-erlangen.de
Department of Physiks, University of Warwick, Coventry CV4 7AL, UK
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
Received/ Accepted
ABSTRACT
Hypervelocity stars (HVS) move so fast that they are unbound to the Galaxy. When they were first discovered in 2005, dynamical
ejection from the supermassive black hole (SMBH) in the Galactic Centre (GC) was suggested as their origin. The two dozen HVSs
known today are young massive B stars, mostly of 3–4 solar masses. Recently, 20 HVS candidates of low mass were discovered in
the Segue G and K dwarf sample, but none of them originates from the GC. We embarked on a kinematic analysis of the Segue HVS
candidate sample using the full 6D phase space information based on new proper motion measurements. Their orbital properties can
then be derived by tracing back their trajectories in different mass models of our Galaxy. We present the results for 14 candidate
HVSs, for which proper motion measurements were possible. Significantly lower proper motions than found in the previous study
were derived. Considering three different Galactic mass models we find that all stars are bound to the Galaxy. We confirm that the
stars do not originate from the GC. The distribution of their proper motions and radial velocities is consistent with predictions for
runaway stars ejected from the Galactic disk by the binary supernova mechanism. However, their kinematics are also consistent with
old disk membership. Moreover, most stars have rather low metallicities and strong α-element enrichment as typical for thick disk
and halo stars, whereas the metallicity of the three most metal-rich stars could possibly indicate that they are runaway stars from the
thin disk. One star shows halo kinematics.
Key words. stars: kinematics and dynamics – stars: low-mass – stars: late-type – stars: abundances – stars: Population II
1. Introduction
The high space velocities and large distances of hypervelocity
stars (HVS) unbound to the Galaxy make them important probes
to map the Galactic dark matter halo. When HVSs were first discovered (Brown et al. 2005; Hirsch et al. 2005; Edelmann et al.
2005), the tidal disruption of a binary by the supermassive black
hole (SMBH) in the Galactic Centre (GC) was suggested as their
origin (Hills 1988). Brown et al. (2014) carried out a systematic
survey for B-type stars in the halo and found about two dozen
HVSs with intermediate masses in the range of 3 to 4 M . As
such stars are luminous their survey covered a large volume (out
to 100 kpc from the GC). Low-mass stars on the other hand can
be accelerated more easily and may gain higher ejection velocities (Tauris 2015). Since they are long-lived they can travel very
large distances during their main-sequence lifetime. However,
they are less luminous than the B-type HVSs and can only be
detected in a smaller volume by flux-limited surveys (<10 kpc),
such as Sloan Extension for Galactic Understanding and Exploration (SEGUE). Moreover, a photometric pre-selection of
low mass main-sequence stars is very difficult because of the
overwhelmingly large number of red stars in the halo. Therefore attempts have been made to isolate HVS candidates of low
mass from the SEGUE G and K Dwarf Sample (Palladino et al.
2014, hereafter P14), LAMOST (Zhong et al. 2014) and RAVE
(Hawkins et al. 2015) surveys using proper motion criteria.
P14 carried out a search for G and K candidate-HVS from the
SEGUE. High proper motion stars were selected for a detailed
analysis of the 6D phase space information and 20 candidates
were found likely to be unbound, four of which at 3σ and six at
2σ significance levels. Calculating the stars’ trajectories in the
Galactic potential P14 derived possible places of origin in the
Galactic disk. Amongst the seven stars with the highest probability of being unbound (> 98%) none crossed the disk near
the GC, but at distances of 5 to 10 kpc away from it. Hence, an
origin in the GC was excluded for those stars, challenging the
SMBH slingshot mechanism. Other ejection mechanisms were
discussed including the classical scenarii for dynamical interaction in star clusters and the binary supernova scenario (Blaauw
1961). The latter has been revisited by Tauris (2015) to derive the
maximum speed of HVS stars ejected from binaries. The simulations indicate that Galactic rest-frame velocities of up to 1280
kms−1 are possible. Such high velocities can explain many, if not
all, of the G/K-dwarf HVSs in the SEGUE sample.
As stressed by P14, the HVS nature of the stars depends
strongly on the proper motion adopted. Therefore, the data was
carefully checked for reliability by simulations. Three stars met
all criteria and therefore were characterized as “clean”. The remaining 17 stars were regarded as “reliable”. P14 found that the
candidates’ tangential velocities are much higher than their radial velocities unlike expected for an isotropic distribution of
stars. The authors therefore caution that the high tangential- vs.
radial-velocity ratio may be characteristic for a sample with large
proper motion errors and built a Monte Carlo test to estimate the
chance of the stars being outliers. All stars show a likelihood of
less than 25%, half of them even less than 10%. Nevertheless, an
independent determination of the proper motions is required.
Article number, page 1 of 6
Generation of the magnetic helicity in
a neutron star driven by the
electroweak electron-nucleon
interaction
Maxim Dvornikova,b,c Victor B. Semikozb
a Institute
of Physics, University of S˜
ao Paulo, CP 66318, CEP 05315-970 S˜
ao Paulo, SP,
Brazil
b Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation (IZMIRAN), 142190 Troitsk, Moscow, Russia
c Physics Faculty, National Research Tomsk State University, 36 Lenin Ave., 634050 Tomsk,
Russia
E-mail: maxim.dvornikov@usp.br, semikoz@yandex.ru
Abstract. We study the instability of magnetic fields in a neutron star core driven by the
parity violating part of the electron-nucleon interaction in the Standard Model. Assuming a
seed field of the order 1012 G, that is a common value for pulsars, one obtains its amplification
due to such a novel mechanism by about five orders of magnitude, up to 1017 G, at time scales
∼ (103 − 105 ) yr. This effect is suggested to be a possible explanation of the origin of the
strongest magnetic fields observed in magnetars. The growth of a seed magnetic field energy
density is stipulated by the corresponding growth of the magnetic helicity density due to the
presence of the anomalous electric current in the Maxwell equation. Such an anomaly is the
sum of the two competitive effects: (i) the chiral magnetic effect driven by the difference of
chemical potentials for the right and left handed massless electrons and (ii) constant chiral
electroweak electron-nucleon interaction term, which has the polarization origin and depends
on the constant neutron density in a neutron star core. The remarkable issue for the decisive
role of the magnetic helicity evolution in the suggested mechanism is the arbitrariness of
an initial magnetic helicity including the case of non-helical fields from the beginning. The
tendency of the magnetic helicity density to the maximal helicity case at large evolution times
provides the growth of a seed magnetic field to the strongest magnetic fields in astrophysics.
Keywords: Chern-Simons term, magnetic fields, magnetic helicity, neutron star
c ESO 2015
Astronomy & Astrophysics manuscript no. RWaur˙revised
March 16, 2015
Another deep dimming of the classical T Tauri star RW Aur A ?
(Research Note)
P. P. Petrov1 , G. F. Gahm2 , A. A. Djupvik3 , E. V. Babina1 , S. A. Artemenko1 , and K. N. Grankin1
1
Crimean Astrophysical Observatory, p/o Nauchny, 298409 Republic of Crimea
email: petrov@crao.crimea.ua; petrogen@rambler.ru
2
Stockholm Observatory, AlbaNova University Centre, Stockholm University, SE-106 91 Stockholm, Sweden
3
Nordic Optical Telescope, Rambla José Ana Fernández Pérez 7, ES-38711 Breña Baja, Spain
ABSTRACT
Context. RW Aur A is a classical T Tauri star (CTTS) with an unusually rich emission line spectrum. In 2014 the star faded by ∼3
magnitudes in the V band and went into a long-lasting minimum. In 2010 the star suffered from a similar fading, although less deep.
These events in RW Aur A are very unusual among the CTTS, and have been attributed to occultations by passing dust clouds.
Aims. We want to find out if any spectral changes took place after the last fading of RW Aur A with the intention to gather more
information on the occulting body and the cause of the phenomenon.
Methods. We collected spectra of the two components of RW Aur. Photometry was made before and during the minimum.
Results. The overall spectral signatures reflecting emission from accretion flows from disk to star did not change after the fading.
However, blue-shifted absorption components related to the stellar wind had increased in strength in certain resonance lines, and the
profiles and strengths, but not fluxes, of forbidden lines had become drastically different.
Conclusions. The extinction through the obscuring cloud is grey indicating the presence of large dust grains. At the same time, there
are no traces of related absorbing gas. The cloud occults the star and the interior part of the stellar wind, but not the wind/jet further
out. The dimming in 2014 was not accompanied by changes in the accretion flows at the stellar surface. There is evidence that the
structure and velocity pattern of the stellar wind did change significantly. The dimmings could be related to passing condensations in
a tidally disrupted disk, as proposed earlier, but we also speculate that large dust grains have been stirred up from the inclined disk
into the line-of-sight through the interaction with an enhanced wind.
Key words. stars: pre-main sequence – stars: variables: T Tau – stars: circumstellar matter – stars: individual: RW Aur
1. Introduction
The classical T Tauri star (CTTS) RW Aur A stands out among
the low-mass pre-main-sequence (PMS) stars with its unusually
rich emission line spectrum as noted early by Joy (1945). The
star has been subject to a large number of investigations. Several
spectral features respond to changes in the accretion rate, like
narrow components in emission lines of e.g. He i, excess continuous emission (called veiling), and red-shifted absorption components flanking certain strong emission lines. These signatures
are prominent in RW Aur A and indicate that the accretion from
a circumstellar disk is heavy and variable (e.g., Petrov et al.
2001; hereafter called P2001). RW Aur is a visual binary with
a separation of 1.400 , where the faint component B is a weak-line
TTS, a PMS star with little or no evidence of accretion.
In 2010, RW Aur A went through a deep minimum reaching
an amplitude of ∼2 magnitudes in V and which lasted for 180
days (Rodriguez et al. 2013; hereafter called R2013). They attributed this drop to an occultation by part of a tidally disrupted
disk as evidenced in Cabrit et al. (2006) and noted that such a
long-lasting event had never been observed before in at least 50
years. Chou et al. (2013) collected high-resolution spectra durSend offprint requests to: P. P. Petrov
?
Based on observations collected at the Nordic Optical Telescope,
La Palma, Spain; Fast-Track Service program 50-409.
ing the beginning of the minimum indicating that no significant
changes in the emission line spectrum had occurred.
Normally, the star fluctuates in brightness by sometimes
more than one magnitude in the V band and on time scales of
a few days. No distinct period has been found as summarised
in e.g. Gahm et al. (1993) and R2013. However, colour changes
with periods of 2.7 to 2.8 days have been reported (Petrov et
al. 2001, R2013), which is close to half the expected rotational
period of about 5.6 days as determined from variations of the
longitudal magnetic field of the star (Dodin et al. 2012). The
star becomes redder with decreasing brightness, and the frequent
drops in brightness from an average level of V ≈ 10.4 appears
to be, at least in part, related to variable foreground extinction
(e.g., Herbst et al. 1994).
In 2014, RW Aur A entered a second long-lasting minimum
in brightness, and this time even deeper than in 2010. According
to the data collected by the American Association of Variable
Star Observers (AAVSO) the brightness dropped by more than 2
magnitudes between May 1 and October 23. Resolved U BVRI
photometry of both components of RW Aur was performed on
November 13/14 2014 by Antipin et al. (2015). They found that
RW Aur A was ∼3 magnitudes fainter in all bands compared to
normal levels and that the star was fainter than component B on
this date. Furthermore, they concluded that the drop in brightness was caused by an increase in foreground, mainly grey extinction.
1
Astronomy & Astrophysics manuscript no. wasp19_sedaghati
March 16, 2015
c
ESO
2015
Letter to the Editor
Regaining the FORS: optical ground-based transmission
spectroscopy of the exoplanet WASP-19b with VLT+FORS2
E. Sedaghati1, 2 , H.M.J. Boffin1 , Sz. Csizmadia2 , N. Gibson3 ,
P. Kabath4 , M. Mallonn5 , and M.E. Van den Ancker3
1
2
3
4
5
ESO, Alonso de Córdova 3107, Casilla 19001, Santiago, Chile
e-mail: esedagha@eso.org; hboffin@eso.org
Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt, Rutherfordstr. 2, 12489 Berlin, Germany
ESO, Karl-Schwarzschild-str. 2, 85748 Garching, Germany
Astronomical Institute ASCR, Friˇcova 298, Ondˇrejov, Czech Republic
Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
Received February 5, 2015; accepted March 12, 2015
ABSTRACT
Since a few years, the study of exoplanets has evolved from being purely discovery and exploratory in nature to being quite quantitative. In particular, transmission spectroscopy now allows the study of exoplanetary atmospheres. Such studies rely heavily on
space-based or large ground-based facilities, as one needs to perform time-resolved, high signal-to-noise spectroscopy. The very recent exchange of the prisms of the FORS2 atmospheric diffraction corrector on ESO’s Very Large Telescope should allow us to reach
higher data quality than was possible before. With FORS2, we have obtained the first optical ground-based transmission spectrum of
WASP-19b, with a 20 nm resolution in the 550–830 nm range. For this planet, the data set represents the highest resolution transmission spectrum obtained to date. We detect large deviations from planetary atmospheric models in the transmission spectrum redward
of 790 nm, indicating the presence of additional sources of opacity not included in the current atmospheric models for WASP-19b, or
additional, unexplored sources of systematics. Nonetheless, this work shows the new potential of FORS2 to study the atmospheres of
exoplanets in greater detail than has been possible so far.
Key words. Planets and satellites: atmospheres – Techniques: spectroscopic – Instrumentation: spectrographs – Stars: individual:
WASP-19
1. Introduction
Transiting exoplanets provide a wealth of information for
studying planetary atmospheres in detail, particularly via spectroscopy. During a planetary transit, some of the stellar light
passes through the limb of the planetary disc, where the presence of an atmosphere allows its indirect inference. When observed at different wavelengths, the transit depth, directly linked
to the apparent planetary radius, may vary, providing constraints
on the scale height of the atmosphere, the chemical composition and the existence of cloud layers (Seager & Sasselov 1998,
2000; Brown 2001; Burrows 2014). Such measurements require
extremely precise relative photometry in as many wavebands as
possible and as such can only be done using space telescopes or
large ground-based facilities.
The FOcal Reducer and low-dispersion Spectrograph
(FORS2) attached to the 8.2-m Unit Telescope 1, is one of the
workhorse instruments of ESO’s Very Large Telescope (Appenzeller et al. 1998). Using its capability to perform multi-object
spectroscopy, Bean et al. (2010) have shown the potential of
FORS2 in producing transmission spectra for exoplanets even
in the mini-Neptune and super-Earth regime. They obtained the
transmission spectrum of GJ 1214b between wavelengths of 780
and 1,000 nm, showing that the lack of features in this spectrum rules out cloud-free atmospheres composed primarily of
hydrogen. However, except for this pioneering result, all further attempts to use FORS2 for exoplanet transit studies have
apparently failed, most likely due to systematics introduced by
the degradation of the antireflective coating of the prisms of the
longitudinal atmospheric dispersion corrector (LADC; Berta et
al. 2011, see also Moehler et al. 2010). A project was therefore started at ESO Paranal to make use of the available decommissioned twin instrument FORS1 (Boffin et al. 2015). The
FORS2 LADC prisms were replaced by their FORS1 counterparts, which had their coating removed. This resulted in a transmission gain of 0.05 mag in the red to 0.1 mag in the blue, most
likely because the uncoating of the LADC largely eliminates the
contribution of scattered light from the previously damaged antireflective coating. As a further test of the improvement provided by the prism exchange, we also observed a transit of the
exoplanet WASP-19b (Hebb et al. 2010). WASP-19 is a 12.3
magnitude G8V star, hosting a hot Jupiter with a mass of 1.17
Jupiter masses (MJ ) and an orbital period of 0.789 days, making
it the Jupiter-like planet with the shortest orbital period known
and one of the most irradiated hot-Jupiters discovered to date.
Due to its short orbital period, and subsequently brief transit duration of ∼1h30, Wasp-19b was an ideal target for assessing the
impact of the prisms exchange on the FORS2 performance.
2. Observations
We observed WASP-19 between 16 November 2014 05:16 UT
and 08:49 UT with FORS2, under thin cirrus, in multi-object
The Five Year Fermi /GBM Magnetar Burst Catalog
A. C. Collazzi1 , C. Kouveliotou2,3 , A. J. van der Horst2 , G. A. Younes4,2 , Y. Kaneko5 ,
E. Gög˘u
¨¸s5 , L. Lin6 , J. Granot7 , M. H. Finger4 , V. L. Chaplin8 , D. Huppenkothen9,10 ,
A. L. Watts11 , A. von Kienlin12 , M. G. Baring13 , D. Gruber14 , P. N. Bhat15 , M. H. Gibby16 ,
N. Gehrels17 , J. McEnery17 , M. van der Klis11 , R. A. M. J. Wijers11
ABSTRACT
Since launch in 2008, the Fermi Gamma-ray Burst Monitor (GBM) has detected many hundreds of bursts from magnetar sources. While the vast majority
of these bursts have been attributed to several known magnetars, there is also
1
SciTec, Inc., 100 Wall Street, Princeton, NJ 08540, USA, acollazzi@scitec.com
2
Department of Physics, The George Washington University, 725 21st Street NW, Washington, DC 20052,
USA
3
Space Science Office, ZP12, NASA/Marshall Space Flight Center, Huntsville, AL 35812, USA
4
Universities Space Research Association, NSSTC, 320 Sparkman Drive, Huntsville, AL 35805, USA
5
˙
Sabancı University, Orhanlı-Tuzla, Istanbul
34956, Turkey
6
Fran¸cois Arago Centre, APC, 10 rue Alice Domon et Léonie Duquet, F-75205 Paris, France
7
Department of Natural Sciences, The Open University of Israel, 1 University Road, P.O. Box 808,
Raanana 43537, Israel
8
School of Medicine, Vanderbilt University, 1161 21st Ave S, Nashville, TN 37232, USA
9
Center for Data Science, New York University, 726 Broadway, 7th Floor, New York, NY 10003
10
Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington
Place, New York, NY 10003
11
Anton Pannekoek Institute, University of Amsterdam, Postbus 94249, 1090 GE Amsterdam, The Netherlands
12
Max-Planck-Institut f¨
ur extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
13
Department of Physics and Astronomy, Rice University, MS-108, P.O. Box 1892, Houston, TX 77251,
USA
14
Planetarium S¨
udtirol, Gummer 5, 39053 Karneid, Italy
15
CSPAR, University of Alabama in Huntsville, 320 Sparkman Dr., Huntsville, AL 35899, USA
16
Jacobs Technology, Inc., Huntsville, AL, USA
17
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Draft version March 16, 2015
Preprint typeset using LATEX style emulateapj v. 5/2/11
HAT-P-50b, HAT-P-51b, HAT-P-52b, AND HAT-P-53b: THREE TRANSITING HOT JUPITERS AND A
TRANSITING HOT SATURN FROM THE HATNET SURVEY.†
´ Bakos1,2 , A. Bieryla3 , G. Kova
´ cs4 , D. W. Latham3 , Z. Csubry1 ,
J. D. Hartman1 , W. Bhatti1 , G. A.
1
1
3,5
3
M. de Val-Borro , K. Penev , L. A. Buchhave , G. Torres , A. W. Howard6 , G. W. Marcy7 , J. A. Johnson3 ,
H. Isaacson7 , B. Sato8 , I. Boisse9 , E. Falco3 , M. E. Everett10 , T. Szklenar11 , B. J. Fulton6 , A. Shporer12 ,
´ cs4,1,14 , T. Hansen13 , B. B´
´ za
´ r11 , I. Papp11 , P. Sa
´ ri11
T. Kova
eky3 , R. W. Noyes3 , J. La
ABSTRACT
We report the discovery and characterization of four transiting exoplanets by the HATNet survey.
The planet HAT-P-50b has a mass of 1.35 MJ and radius of 1.29 RJ , and orbits a bright (V = 11.8 mag)
M = 1.27 M⊙ , R = 1.70 R⊙ star every P = 3.1220 days. The planet HAT-P-51b has a mass of 0.31 MJ
and radius of 1.29 RJ , and orbits a V = 13.4 mag, M = 0.98 M⊙ , R = 1.04 R⊙ star with a period
of P = 4.2180 days. The planet HAT-P-52b has a mass of 0.82 MJ and radius of 1.01 RJ , and orbits
a V = 14.1 mag, M = 0.89 M⊙ , R = 0.89 R⊙ star with a period of P = 2.7536 days. The planet
HAT-P-53b has a mass of 1.48 MJ and radius of 1.32 RJ , and orbits a V = 13.7 mag, M = 1.09 M⊙ ,
R = 1.21 R⊙ star with a period of P = 1.9616 days. All four planets are consistent with having
circular orbits and have masses and radii measured to better than 10% precision. The low stellar
jitter and favorable Rp /R⋆ ratio for HAT-P-51 make it a promising target for measuring the RossiterMcLaughlin effect for a Saturn-mass planet.
Subject headings: planetary systems — stars: individual ( HAT-P-50, GSC 0787-00340, HAT-P51, GSC 2296-00637, HAT-P-52, GSC 1793-01136, HAT-P-53, GSC 2813-01266 )
techniques: spectroscopic, photometric
1 Department of Astrophysical Sciences, Princeton University,
Princeton, NJ 08544; email: jhartman@astro.princeton.edu
2 Sloan and Packard Fellow
3 Harvard-Smithsonian Center for Astrophysics, Cambridge,
MA 02138
4 Konkoly Observatory, Budapest, Hungary
5 Niels Bohr Institute, University of Copenhagen, DK-2100,
Denmark, and Centre for Star and Planet Formation, National
History Museum of Denmark, DK-1350 Copenhagen
6 Institute for Astronomy, University of Hawaii, Honolulu, HI
96822
7 Department of Astronomy, University of California, Berkeley, CA
8 Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8550, Japan
9 Aix Marseille Universit´
e, CNRS, LAM (Laboratoire
d’Astrophysique de Marseille) UMR 7326, 13388, Marseille,
France
10 National Optical Astronomy Observatory, 950 N. Cherry
Ave, Tucson, AZ 85719
11 Hungarian Astronomical Association, Budapest, Hungary
12 Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109
13 Landessternwarte, ZAH, K¨
onigstuhl 12, D-69117 Heidelberg, Germany
14 Fulbright Fellow
† Based on observations obtained with the Hungarian-made
Automated Telescope Network. Based on observations obtained
at the W. M. Keck Observatory, which is operated by the University of California and the California Institute of Technology.
Keck time has been granted by NOAO (A245Hr) and NASA
(N154Hr, N130Hr). Based on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. Based on observations made with the Nordic
Optical Telescope, operated on the island of La Palma jointly
by Denmark, Finland, Iceland, Norway, Sweden, in the Spanish
Observatorio del Roque de los Muchachos of the Instituto de
Astrof´ısica de Canarias. Based on observations obtained with
the Tillinghast Reflector 1.5 m telescope and the 1.2 m telescope,
both operated by the Smithsonian Astrophysical Observatory at
the Fred Lawrence Whipple Observatory in AZ. Based on radial
velocities obtained with the Sophie spectrograph mounted on the
1.93 m telescope at Observatoire de Haute-Provence. Based on
observations obtained with facilities of the Las Cumbres Observatory Global Telescope.
Image patch analysis of sunspots and active
regions. I. Intrinsic dimension and correlation
analysis
Kevin R. Moon1 , Jimmy J. Li1 , Véronique Delouille2 , Ruben De Visscher2 , Fraser
Watson3 , and Alfred O. Hero III1
1
2
3
Electrical Engineering and Computer Science Department, University of Michigan
SIDC, Royal Observatory of Belgium
National Solar Observatory
Abstract
Context. Complexity of an active region is related to its flare-productivity. Mount Wilson or
McIntosh sunspot classifications measure such complexity but in a categorical way, and may therefore not use all the information present in the observations. Moreover, such categorical schemes
hinder a systematic study of an active region’s evolution for example.
Aims. We propose fine-scale quantitative descriptors for an active region’s complexity and relate
them to the Mount Wilson classification. We analyze the local correlation structure within continuum and magnetogram data, as well as the cross-correlation between continuum and magnetogram
data.
Methods. We compute the intrinsic dimension, partial correlation and canonical correlation analysis (CCA) of image patches of continuum and magnetogram active region images taken from
the SOHO-MDI instrument. We use masks of sunspots derived from continuum as well as larger
masks of magnetic active regions derived from magnetogram to analyze separately the core part of
an active region from its surrounding part.
Results. We find relationships between the complexity of an active region as measured by its
Mount Wilson classification and the intrinsic dimension of its image patches. Partial correlation
patterns exhibit approximately a third-order Markov structure. CCA reveals different patterns of
correlation between continuum and magnetogram within the sunspots and in the region surrounding the sunspots.
Conclusions. Intrinsic dimension has the potential to distinguish simple from complex active regions. These results also pave the way for patch-based dictionary learning with a view towards
automatic clustering of active regions.
Key words. Sun – active region – sunspot – data analysis – classification – image patches –
intrinsic dimension – partial correlation – CCA
1
To be published in the Astrophysical Journal
Revealing δ Cephei’s Secret Companion and Intriguing Past
R.I. Anderson1,2,4 , J. Sahlmann3 , B. Holl2 , L. Eyer2 , L. Palaversa2 , N. Mowlavi2 , M.
S¨
uveges2 , M. Roelens2
1
Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218,
USA
2
Département d’Astronomie, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny,
Switzerland
3
European Space Agency, European Space Astronomy Centre, P.O. Box 78, Villanueva de
la Ca˜
nada, 28691 Madrid, Spain
ria@jhu.edu
ABSTRACT
Classical Cepheid variable stars are crucial calibrators of the cosmic distance
scale thanks to a relation between their pulsation periods and luminosities. Their
archetype, δ Cephei, is an important calibrator for this relation. In this paper,
we show that δ Cephei is a spectroscopic binary based on newly-obtained highprecision radial velocities. We combine these new data with literature data to
determine the orbit, which has period 2201 days, semi-amplitude 1.5 km s−1 , and
high eccentricity (e = 0.647). We re-analyze Hipparcos intermediate astrometric
data to measure δ Cephei’s parallax ($ = 4.09 ± 0.16 mas) and find tentative
evidence for an orbital signature, although we cannot claim detection. We estimate that Gaia will fully determine the astrometric orbit. Using the available
information from spectroscopy, velocimetry, astrometry, and Geneva stellar evolution models (MδCep ∼ 5.0 − 5.25 M ), we constrain the companion mass to
within 0.2 < M2 < 1.2 M . We discuss the potential of ongoing and previous interactions between the companion and δ Cephei near pericenter passage,
informing reported observations of circumstellar material and bow-shock. The
orbit may have undergone significant changes due to a Kozai-Lidov mechanism
4
Swiss National Science Foundation Fellow
c
ESO
2015
Astronomy & Astrophysics manuscript no. AB_Aur_final
March 16, 2015
Chemical composition of the circumstellar disk around AB Aurigae
S. Pacheco-Vázquez1 , A. Fuente1 , M. Agúndez2 , C. Pinte6 , T. Alonso-Albi1 , R. Neri3 , J. Cernicharo2 , J. R.
Goicoechea2 , O. Berné4, 5 , L. Wiesenfeld6 , R. Bachiller1 , and B. Lefloch6
1
2
3
4
5
6
Observatorio Astronómico Nacional (OAN), Apdo 112, E-28803 Alcalá de Henares, Madrid, Spain
e-mail: s.pacheco@oan.es, a.fuente@oan.es, t.alonso@oan.es
Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC, C/ Sor Juana Inés de la Cruz 3, E-28049 Cantoblanco, Spain
e-mail: marcelino.agundez@icmm.csic.es,jcernicharo@cab.inta-csic.es, jr.goicoechea@cab.inta-csic.es
Institut de Radioastronomie Millimétrique, 300 Rue de la Piscine, F-38406 Saint Martin d’Hères, France
e-mail: neri@iram.fr
Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
CNRS, IRAP, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4, France e-mail: olivier.berne@gmail.com
Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Université UJF-Grenoble 1/CNRS-INSU, F-38041
Grenoble, France
e-mail: laurent.wiesenfeld@ujf-grenoble.fr, Bertrand.Lefloch@obs.ujf-grenoble.fr
Received September 15, 1996; accepted March 16, 1997
ABSTRACT
Aims. Our goal is to determine the molecular composition of the circumstellar disk around AB Aurigae (hereafter, AB Aur). AB Aur
is a prototypical Herbig Ae star and the understanding of its disk chemistry is of paramount importance to understand the chemical
evolution of the gas in warm disks.
Methods. We used the IRAM 30-m telescope to perform a sensitive search for molecular lines in AB Aur as part of the IRAM Large
program ASAI (A Chemical Survey of Sun-like Star-forming Regions). These data were complemented with interferometric observations of the HCO+ 1→0 and C17 O 1→0 lines using the IRAM Plateau de Bure Interferometer (PdBI). Single-dish and interferometric
data were used to constrain chemical models.
Results. Throughout the survey, several lines of CO and its isotopologues, HCO+ , H2 CO, HCN, CN and CS, were detected. In
addition, we detected the SO 54 →33 and 56 →45 lines, confirming the previous tentative detection. Comparing to other T Tauri’s and
Herbig Ae disks, AB Aur presents low HCN 3→2/HCO+ 3→2 and CN 2→1/HCN 3→2 line intensity ratios, similar to other transition
disks. AB Aur is the only protoplanetary disk detected in SO thus far, and its detection is consistent with the interpretation of this disk
being younger than those associated with T Tauri stars.
Conclusions. We modeled the line profiles using a chemical model and a radiative transfer 3D code. Our model assumes a flared
disk in hydrostatic equilibrium. The best agreement with observations was obtained for a disk with a mass of 0.01 M⊙ , Rin =110 AU,
Rout =550 AU, a surface density radial index of 1.5 and an inclination of 27◦ . The intensities and line profiles were reproduced within
a factor of ∼2 for most lines. This agreement is reasonable taking into account the simplicity of our model that neglects any structure
within the disk. However, the HCN 3→2 and CN 2→1 line intensities were predicted more intense by a factor of >10. We discuss
several scenarios to explain this discrepancy.
Key words. stars: formation – stars: individual: AB Aur – stars: pre-main sequence – stars: variables: T Tauri, Herbig Ae/Be –
circumstellar matter – protoplanetary disks
1. Introduction
Circumstellar disks are commonly observed around pre-main sequence stars (e.g., Howard et al. 2013; Strom et al. 1989). The
formation of disks, together with ejecta phenomena such as outflows and jets, dissipate away the excess of angular momentum
that prevents accretion from the parent cloud. The chemical composition of dust and gas contained in these disks provides information about the initial conditions in the formation of planetary
systems (Dutrey et al. 2014).
The comprehension of chemistry in disks is an important step
in the understanding of the formation of complex organic, even
prebiotic molecules, on planets. However, the disk chemistry is a
quite unexplored field from the observational point of view with
very few molecular detections. This scarcity of molecules seems
more accentuated in disks around Herbig Ae stars (Öberg et al.
2011). This is mainly due to the low molecular abundances in
a gas disk which itself has a low mass content. The ultraviolet
radiation from the central star photodissociates molecules in the
surface layers of the disk. Deeper in the midplane, the temperatures drop and all the detectable molecules freeze out onto dust
grains. Hence, molecules can survive only in the gas phase inside a thin layer. For F and A stars with effective temperatures
in the range between 6000 to 10000 K, the UV-photons penetrate deeper into the disk than the colder M and K stars (Teff
∼ 2500 - 5000K), causing the drop of the molecular detection
rates. Most species detected are simple molecules, molecular
radicals and ions such as CO, 13 CO, C18 O, CN, CS, C34 S, C2 H,
HCN, H13 CN, HNC, DCN, HC3 N, HCO+ , H13 CO+ , DCO+ ,
H2 D+ , N2 H+ , c-C3 H2 , H2 CO, H2 O and HD (e.g., Kastner et al.
1997; van Dishoeck et al. 2003; Thi et al. 2004; Qi et al. 2008;
Guilloteau et al. 2006; Piétu et al. 2007; Dutrey et al. 2007).
Unfortunately most disks remain unresolved even with the
largest millimeter interferometers. A detailed study of the chemArticle number, page 1 of 15
c ESO 2015
Astronomy & Astrophysics manuscript no. mdwarf˙v13
March 16, 2015
New evolutionary models for pre-main sequence and main
sequence low-mass stars down to the hydrogen-burning limit
Isabelle Baraffe1,2 , Derek Homeier2 , France Allard2 , and Gilles Chabrier2,1
1
2
University of Exeter, Physics and Astronomy, EX4 4QL Exeter, UK (e-mail: i.baraffe@ex.ac.uk)
´
Ecole
Normale Supérieure, Lyon, CRAL (UMR CNRS 5574), Université de Lyon, France
derek.homeier@ens-lyon.fr, fallard@ens-lyon.fr, chabrier@ens-lyon.fr)
(e-mail:
ABSTRACT
We present new models for low-mass stars down to the hydrogen-burning limit that consistently couple atmosphere and
interior structures, thereby superseding the widely used BCAH98 models. The new models include updated molecular
linelists and solar abundances, as well as atmospheric convection parameters calibrated on 2D/3D radiative hydrodynamics simulations. Comparison of these models with observations in various colour-magnitude diagrams for various
ages shows significant improvement over previous generations of models. The new models can solve flaws that are
present in the previous ones, such as the prediction of optical colours that are too blue compared to M dwarf observations. They can also reproduce the four components of the young quadruple system LkCa 3 in a colour-magnitude
diagram with one single isochrone, in contrast to any presently existing model. In this paper we also highlight the need
for consistency when comparing models and observations, with the necessity of using evolutionary models and colours
based on the same atmospheric structures.
Key words. stars: low-mass - stars: evolution - stars: pre-main sequence - stars: Hertzsprung-Russell diagrams and C-M
diagrams - convection
1. Introduction
In 1998, our team released a set of evolutionary models for low-mass stars (Baraffe et al., 1998, hereafter
BCAH98) based on the so-called NextGen atmosphere
models (Hauschildt et al., 1999) that marked a new era
of models that consistently coupled interior and atmosphere structures. These models became very popular because they successfully reproduce various observational
constraints, such as mass-luminosity and mass-radius relationships and colour-magnitude diagrams. The models,
however, had some important shortcomings, such as predicting optical (V −I) colours that are too blue for a given
magnitude (see §3.1). Later generations of models included
improved molecular linelists for various atmospheric absorbers, such as the AMES linelists used in the Dusty and
Cond models (Chabrier et al., 2000; Allard et al., 2001;
Baraffe et al., 2003), but they still show shortcomings (see
§3.2). After a long effort to solve these flaws, efforts have
paid off with the release of current models that supersede
the BCAH98 models. In this paper, we describe the main
physical ingredients of the models and compare them to a
selection of observations that highlight the improvement of
these new models over previous ones.
2. Model description
Evolutionary calculations are based on the same input
physics describing stellar and substellar interior structures
as are used in Chabrier & Baraffe (1997) and Baraffe et al.
Send offprint requests to: I. Baraffe
(1998). The major changes concern the atmosphere models, which provide the outer boundary conditions for the
interior structure calculation, and the colours and magnitudes for a given star mass at any given age. Substantial
changes have been made since the NextGen atmosphere
models used in the BCAH98 evolutionary models. A preliminary set of atmosphere models, referred to as the BT-Settl
models (Allard et al., 2012a,b; Rajpurohit et al., 2013), include some of these changes, which are briefly summarised
below. More recent modifications concerning the treatment
of convection are described in §2.3.
2.1. Molecular linelists and cloud formation
Line opacities for several important molecules have been
updated, notably the water linelist from Barber et al.
(2006), metal hydrides such as CaH, FeH, CrH, TiH from
Bernath (2006), vanadium oxide from Plez (2004, priv.
comm.), and carbon dioxide from Tashkun et al. (2004).
For TiO, the present set of atmosphere models uses the
linelist from Plez (1998). This list is not as complete at high
energies as the AMES linelist (Schwenke, 1998) adopted
in Allard et al. (2001, 2012a), with only 11×106 lines
compared to the 160×106 of Schwenke (1998). But the
Plez linelist reproduces the overall band strengths better
and thus generally improves the optical colours (Fig. 4).
Obviously, the field is still in need of a new, complete,
and accurate theoretical TiO linelist to allow quantitative high-resolution spectroscopic analysis of this important molecule, as recently pointed by the high-resolution
transmission spectrum analysis of a transiting exoplanet
(Hoeijmakers et al., 2014).
1
Journal reference: Icarus 210 (2010) 230-257.
THE SOURCE OF WIDESPREAD 3-µm ABSORPTION IN JUPITER’S CLOUDS: CONSTRAINTS FROM 2000
CASSINI VIMS OBSERVATIONS†
L.A. Sromovsky1 and P.M. Fry1
Journal reference: Icarus 210 (2010) 230-257.
ABSTRACT
The Cassini flyby of Jupiter in 2000 provided spatially resolved spectra of Jupiter’s atmosphere
using the Visual and Infrared Mapping Spectrometer (VIMS). A prominent characteristic of these
spectra is the presence of a strong absorption at wavelengths from about 2.9 µm to 3.1 µm, previously
noticed in a 3-µm spectrum obtained by the Infrared Space Observatory (ISO) in 1996. While Brooke
et al. (1998, Icarus 136, 1-13) were able to fit the ISO spectrum very well using ammonia ice as the sole
source of particulate absorption, Sromovsky and Fry (2010, Icarus 210, 211-229), using significantly
revised NH3 gas absorption models, showed that ammonium hydrosulfide (NH4 SH) provided a better
fit to the ISO spectrum than NH3 , but that the best fit was obtained when both NH3 and NH4 SH were
present in the clouds. Although the large FOV of the ISO instrument precluded identification of the
spatial distribution of these two components, the VIMS spectra at low and intermediate phase angles
show that 3-µm absorption is present in zones and belts, in every region investigated, and both lowand high-opacity samples are best fit with a combination of NH4 SH and NH3 particles at all locations.
The best fits are obtained with a layer of small ammonia-coated particles (r ∼ 0.3 µm) overlying but
often close to an optically thicker but still modest layer of much larger NH4 SH particles (r ∼ 10
µm), with a deeper optically thicker layer, which might also be composed of NH4 SH. Although these
fits put NH3 ice at pressures less than 500 mb, this is not inconsistent with the lack of prominent
NH3 features in Jupiter’s longwave spectrum because the reflectivity of the core particles strongly
suppresses the NH3 absorption features, at both near-IR and thermal wavelengths. Unlike Jupiter,
Saturn lacks the broad 3-µm absorption feature, but does exhibit a small absorption near 2.965 µm,
which resembles a similar Jovian feature and suggests that both planets contain upper tropospheric
clouds of sub-micron particles containing ammonia as a minor fraction.
Subject headings: Jupiter; Jupiter, Atmosphere; Jupiter, Clouds
1. INTRODUCTION
Analysis of Pioneer and groundbased observations of
Jupiter, summarized by West et al. (1986), led to an expected Jovian cloud structure that included an upper
ammonia cloud layer starting near 700-mb and a putative NH4 SH cloud top near 2 bars, which was thought to
be optically thick outside the hot spot regions. The putative ammonia cloud was thought to have two particle
populations: a vertically compact layer of large particles
(of 3 to 100 µm in radius) and a vertically diffuse component of small particles (r ∼ 1µm) extending up to 200300 mb in low latitude regions. However, the more diffuse
component should have produced prominent spectral signatures at 9.4 µm and 26 µm, which were not observed
(Orton et al. 1982). After considering possible masking
of these features by the likely tetrahedral shapes of these
particles, West et al. (1989) concluded that these particles could not be primarily composed of ammonia ice. It
was also the case that neither Voyager Infrared Interferometer Spectrometer (IRIS) observations (Carlson et al.
1993), nor microwave observations (de Pater 1986), ever
found an ammonia vapor profile that would support a
700-mb condensation level. Carlson’s derived condensation pressure was closer to 500 mb, while a later analy1
University of Wisconsin - Madison, Madison WI 53706
Partly based on observations obtained from the data archive
at the Space Telescope Science Institute. STScI is operated by
the Association of Universities for Research in Astronomy, Inc.
under NASA contract NAS 5-26555.
†
sis of microwave observations (de Pater et al. 2001) suggested NH3 condensation near 600 mb.
Only in the last decade or so has there been even a hint
of the spectral signatures expected of NH3 ice clouds.
From an analysis of a 3-µm absorption anomaly in a
central-disk spectrum of Jupiter, Brooke et al. (1998) inferred the existence of a layer of ammonia ice particles
of 10 µm in radius, beginning at 550 mb with a scale
height of 30% of the gas scale height. The wide field of
view covered by the observation (roughly a quarter of the
Jovian disk) suggested that the ammonia ice was widely
distributed. Irwin et al. (2001) found a similar absorption anomaly in analysis of observations by the Galileo
Near Infrared Mapping Spectrometer (NIMS), but concluded that it was not due to NH3 ice because a key spectral signature at 2.0 µm was missing. The subsequent
Baines et al. (2002) detection of spectrally identifiable
ammonia clouds (SIACs) in other NIMS observations was
based on depressed reflectivity at 2.7 µm as well as at
2.0 µm, but these detections covered a very tiny fraction
(< 1%) of Jupiter’s cloud features. On the other hand,
Wong et al. (2004) inferred more widely distributed ammonia ice, at least in some latitude bands, from a detection of a 9.4-µm spectral feature in Jovian spectra obtained from the Cassini Composite Infrared Spectrometer (CIRS). The model calculations of Wong et al. (2004)
implied that the 9.4-µm ice feature could only be detected when the aerosols were at pressures ≤500 mb and
the particle effective radius was within a factor of two of
Preprint typeset in JINST style - HYPER VERSION
arXiv:1503.04096v1 [astro-ph.IM] 13 Mar 2015
An introduction to some imperfections of CCD
sensors
P. Astiera
a
LPNHE/IN2P3/CNRS,
UPMC, 4 place Jussieu F75005 Paris, France
E-mail: pierre.astier@in2p3.fr
A BSTRACT: CCD sensors do not deliver a perfect image of the light they receive. Beyond the
well known linear image smearing due to diffusion of charges during their drift towards the pixel
wells, non-linear effects are at play in these sensors. We now have ample evidence for both a fluxdependent and static image distortions, especially but not only, on deep-depleted CCDs. For large
surveys relying on CCD sensors, these effects should now be taken into account when reducing
data. We present here a summary of current results on sensor characterization and mitigation
methods.
K EYWORDS : Detectors for UV, visible and IR photons (solid-state); Image processing.
On the generation of triaxiality in the collapse of cold
spherical self-gravitating systems
Francesco
Sylos Labini1,2, David Benhaiem1,2 and Michael Joyce3,4
1
Centro Studi e Ricerche Enrico Fermi, Via Panisperna 89 A, Compendio del Viminale, 00184 Rome, Italy
dei Sistemi Complessi Consiglio Nazionale delle Ricerche, Via dei Taurini 19, 00185 Rome, Italy
3 UPMC Univ Paris 06, UMR 7585, LPNHE, F-75005, Paris, France
4 CNRS IN2P3, UMR 7585, LPNHE, F-75005, Paris, France
2 Istituto
16 March 2015
ABSTRACT
Initially cold and spherically symmetric self-gravitating systems may give rise to a
virial equilibrium state which is far from spherically symmetric, and typically triaxial.
We focus here on how the degree of symmetry breaking in the final state depends
on the initial density profile. We note that the most asymmetric structures result
when, during the collapse phase, there is a strong injection of energy preferentially
into the particles which are localized initially in the outer shells. These particles are
still collapsing when the others, initially located in the inner part, are already reexpanding; the motion of particles in a time varying potential allow them to gain
kinetic energy — in some cases enough to be ejected from the system. We show
that this mechanism of energy gain amplifies the initial small deviations from perfect
spherical symmetry due to finite N fluctuations. This amplification is more efficient
when the initial density profile depends on radius, because particles have a greater
spread of fall times compared to a uniform density profile, for which very close to
symmetric final states are obtained. These effects lead to a distinctive correlation of
the orientation of the final structure with the distribution of ejected mass, and also
with the initial (very small) angular fluctuations.
Key words: Cosmological structure formation, gravitational clustering, N -body simulation
1
INTRODUCTION
That self-gravitating systems initially in highly spherically
symmetric configurations can relax to virial equilibria
which break this symmetry strongly has been known
for several decades (Polyachenko & Shukhman 1981;
Merritt & Aguilar 1985) and documented since then by
many numerical studies (see e.g. Aguilar & Merritt (1990);
Theis & Spurzem (1999); Boily & Athanassoula (2006);
Barnes, Lanzel & Williams
(2009);
Worrakitpoonpon
(2014)). This phenomenon, of formation, and argued to play a crucial role in cosmological structure
formation
(see e.g. Huss, Jain & Steinmetz (1999);
MacMillan, Widrow & Henriksen (2006)) has come to be
referred to as “radial orbit instability” (ROI). This name
has been adopted since such an instability has been shown
(Antonov 1961; Fridman et al. 1984) to characterize spherically symmetric stationary solutions of the collisionless
Boltzmann equation with purely radial orbits. Further it is
plausible, as argued originally by Merritt & Aguilar (1985),
that a similar mechanism is responsible for the formation of
triaxial structures observed starting from very cold initial
c 0000 RAS
conditions, as in this case collapse tends to produce strongly
radial orbits. Different authors (see references above) have
discussed how the symmetry breaking develops during the
evolution from both simple power law density profiles (e.g.
Boily & Athanassoula (2006)) and from cosmological initial
conditions (e.g. MacMillan, Widrow & Henriksen (2006).
In this paper we consider how the degree of the final
symmetry breaking is related to the initial condition —
specifically to the exponent of the initial density profile —
for the case of completely cold initial conditions. Our focus on this aspect of the problem allows us to elucidate the
mechanism by which the symmetry breaking actually occurs in the process of collapse from cold initial conditions.
More specifically, we show in detail how fluctuations breaking spherical symmetry may be amplified by the very large
energy changes characteristic of the very violent relaxation
from cold initial conditions. This amplification is most effective when the energy change a particle undergoes is both
large and strongly correlated with its initial radial position,
leading to a maximal effect from density profiles with intermediate exponents. We underline that the mechanism we
Magnetically-Driven Accretion-Disk Winds and Ultra-Fast
Outflows in PG 1211+143
Keigo Fukumura1,2 , Francesco Tombesi3,4 Demosthenes Kazanas3 , Chris
Shrader3,5 , Ehud Behar6 , and Ioannis Contopoulos7
Received
;
accepted
1
Email: fukumukx@jmu.edu
2
James Madison University, Harrisonburg, VA 22807
3
Astrophysics Science Division, NASA/Goddard Space Flight Center, Greenbelt, MD
20771
4
Department of Astronomy and CRESST, University of Maryland, College Park,
MD20742
5
Universities Space Research Association, 7178 Columbia Gateway Dr. Columbia, MD
21046
6
Department of Physics, Technion, Haifa 32000, Israel
7
Research Center for Astronomy, Academy of Athens, Athens 11527, Greece
–2–
ABSTRACT
We present a study of X-ray ionization of magnetohydrodynamic (MHD)
accretion-disk winds in an effort to constrain the physics underlying the highlyionized ultra-fast outflows (UFOs) inferred by X-ray absorbers often detected in
various sub-classes of Seyfert active galactic nuclei (AGNs). Our primary focus is
to show that magnetically-driven outflows are indeed physically plausible candidates for the observed outflows accounting for the AGN absorption properties of
the present X-ray spectroscopic observations. Employing a stratified MHD wind
launched across the entire AGN accretion disk, we calculate its X-ray ionization
and the ensuing X-ray absorption line spectra. Assuming an appropriate ionizing
AGN spectrum, we apply our MHD winds to model the absorption features in
an XMM-Newton/EPIC spectrum of the narrow-line Seyfert, PG 1211+143. We
find, through identifying the detected features with Fe Kα transitions, that the
absorber has a characteristic ionization parameter of log(ξc [erg cm s−1 ]) ≃ 5 − 6
and a column density on the order of NH ≃ 1023 cm−2 , outflowing at a characteristic velocity of vc /c ≃ 0.1 − 0.2 (where c is the speed of light). The best-fit
model favors its radial location at rc ≃ 200Ro (Ro is the black hole innermost
stable circular orbit), with an inner wind truncation radius at Rt ≃ 30Ro . The
overall K-shell feature in the data is suggested to be dominated by Fe xxv with
very little contribution from Fe xxvi and weakly-ionized iron, which is in a good
agreement with a series of earlier analysis of the UFOs in various AGNs including
PG 1211+143.
Subject headings: accretion, accretion disks — galaxies: Seyfert — methods: numerical
— galaxies: individual (PG 1211+143) — X-rays: galaxies
Modeling of the γ-ray pulsed spectra of Geminga, Crab,
and Vela with synchro-curvature radiation
Daniele
Viganò1 & Diego F. Torres1,2
1
Institute of Space Sciences (CSIC–IEEC), Campus UAB, C. de Can Magrans, s/n 08193, Cerdanyola del Valles (Barcelona), Spain
Catalana de Recerca i Estudis Avan¸cats (ICREA), 08010, Barcelona, Spain
2 Instituci´
o
ABSTRACT
γ-ray spectra of pulsars have been mostly studied in a phenomenological way, by fitting
them to a cut-off power-law function. Here, we analyze a model where pulsed emission
comes from synchro-curvature processes in a gap. We calculate the variation of kinetic
energy of magnetospheric particles along the gap and the associated radiated spectra,
considering an effective particle distribution. We fit the phase-averaged and phaseresolved Fermi-LAT spectra of the three brightest γ-ray pulsars: Geminga, Crab, and
Vela, and constrain the three free parameters we leave free in the model. Our best-fit
models well reproduce the observed data, apart from residuals above a few GeV in some
cases, range for which the inverse Compton scattering likely becomes the dominant
mechanism. In any case, the flat slope at low-energy (. GeV) seen by Fermi-LAT
both in the phase-averaged and phase-resolved spectra of most pulsars, including the
ones we studied, requires that most of the detected radiation below ∼GeV is produced
during the beginning of the particle trajectories, when radiation mostly come from the
loss of perpendicular momentum.
1
INTRODUCTION
The wealth of Fermi-LAT data (Abdo et al. 2013) has
boosted our knowledge about γ-ray emission from pulsars,
allowing a better understanding of the fundamental highenergy processes which are responsible for the conversion
of the rotational energy into radiation. Two main channels
are the likely origin of the detected radiation: photons emitted by particles moving in curved magnetic fields and accelerating electric fields, i.e., the synchro-curvature (SC) radiation, and the inverse Compton (IC) scattering of background photons against energetic magnetospheric particles
(Bogovalov & Aharonian 2000).
This paper is the continuation of a series of works
(Vigan`
o et al. 2015a,b,c), in which we focus on the highenergy SC radiation, and to which we refer the reader for
further details. Our approach applies to any general gap
located in the outer magnetosphere (even outside the light
cylinder), since our parameters do not depend on an a-priori,
detailed choice of the location of the gap. Instead, we show
here how data can be used to constrain the values of the
most relevant gap parameters of the model.
The E 2 dN/dE spectra of pulsed γ-ray emission from
most pulsars peak around a few GeV, above which the flux
quickly decreases with energy. Spectra are usually described
by a cut-off power-law:
s dP
E
µ
,
(1)
= P0 E exp −
dE
Ep
where the four parameters to be fit are the normalization
P0 , the low-energy slope index µ, the peak energy Ep , and
the exponential index s. The values of the best-fit models
give a µ-range in the interval (−1, 0.5), with the distribution
peaking close to µ ∼ −0.5 (see Fig. 7 of Abdo et al. 2013,
where their Γ is related to µ as Γ = 1 − µ). This relative
flatness at low energies (0.1-1 GeV) contrasts with the value
of µ predicted by the SC spectrum of a single-particle, which
has a value µ = 0.25 due to mathematical properties of
the functions involved. The latter is consistent only with a
small minority of observed pulsars. This fact means that a
simple SC radiation model which considers a mono-energetic
distribution of particles is unable on a first-principle-basis to
explain most of the observed spectra.
The relative flatness (i.e., µ ∼ −1) of many pulsar spectra at low Fermi-LAT energies is a basic issue that to our
knowledge has never been properly addressed. In particular, we believe it could signal that non-saturated particles are important contributors to the total emitted radiation. Put otherwise, that the contribution of different parts
of the particle trajectories is non-uniform. In Vigan`
o et al.
(2015a,c) we showed how a large weight given to the initial parts of the trajectories, where the radiation is dominated by synchrotron-like emission, can explain flatter slopes
(µ < 0.25). We study this possibility in more detail here, and
advance that it is in agreement with data.
Pulsar spectra show another important feature: for
some sources, the phase-averaged spectrum shows a subexponential cut-off, i.e., s < 1. The high-energy tail (E &
few GeV) decreases in energy slower than a the expected SC
radiation emitted by mono-energetic particles, which produces a purely exponential cut-off, s = 1. This issue alone
does not rule out SC radiation as the dominant mechanism:
the phase-averaged spectrum is the super-position of radi-
New Cosmographic Constraints
on the Dark Energy and Dark Matter Coupling
Yu.L. Bolotin1 , V.A. Cherkaskiy2 , O.A. Lemets3
A.I.Akhiezer Institute for Theoretical Physics, National Science Center ”Kharkov Institute
of Physics and Technology”, Akademicheskaya Str. 1, 61108 Kharkov, Ukraine
Abstract
We consider some models describing interaction between the dark components
and obtain an expression for the coupling constant which contains only the
cosmographic parameters. It enables us on the one hand to find constrains
on the coupling constants using observational data, and on the other hand,
given fixed constraints on the coupling, to restrict number of numerous models
describing the interaction in the dark sector.
Keywords: cosmographic parameters, interaction in the dark sector
Introduction
Typically, dark energy (DE) models are based on scalar fields minimally
coupled to gravity, and do not implement the explicit coupling of the field to
the background matter [1, 2]. However there is no fundamental reason for this
assumption in the absence of an underlying symmetry which would suppress the
coupling. Given that we do not know the true nature of neither DE nor dark
matter (DM) one cannot exclude that there exists a coupling between them.
Whereas new forces between DE and normal matter particles are heavily constrained by observations (e.g. in the solar system and gravitational experiments
on Earth), this is not the case for DM particles. In other words, it is possible
1 ybolotin@gmail.com
2 vcherkaskiy@gmail.com
3 oleg.lemets@gmail.com
Preprint submitted to Physics Letters B
March 16, 2015
Vertical convection in neutrino-dominated accretion flows
Tong Liu1,2,3,4 , Wei-Min Gu1,4 , Norita Kawanaka5 , and Ang Li1,3,4
tongliu@xmu.edu.cn
ABSTRACT
We present the effects of the vertical convection on the structure and luminosity of the neutrino-dominated accretion flow (NDAF) around a stellar-mass black
hole in spherical coordinates. We found that the convective energy transfer can
suppress the radial advection in the NDAF, and that the density, temperature
and opening angle are slightly changed. As a result, the neutrino luminosity and
annihilation luminosity are increased, which is conducive to achieve the energy
requirement of gamma-ray bursts.
Subject headings: accretion, accretion disks - black hole physics - convection gamma-ray burst: general - neutrinos
1.
Introduction
The central engine of gamma-ray bursts (GRBs) is usually modelled as the system
consisting of a rapidly spinning stellar black hole and an extremely optically thick disk
with high density and temperature, namely neutrino-dominated accretion flow (NDAF). The
neutrino radiation is the main cooling mechanism, which possibly has the ability to power
GRBs via neutrino annihilation outside the disk. A lot of works on this model had been done
1
Department of Astronomy and Institute of Theoretical Physics and Astrophysics, Xiamen University,
Xiamen, Fujian 361005, China; tongliu@xmu.edu.cn
2
Key Laboratory for the Structure and Evolution of Celestial Objects, Chinese Academy of Sciences,
Kunming, Yunnan 650011, China
3
State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of
Sciences, Beijing 100190, China
4
5
SHAO-XMU Joint Center for Astrophysics, Xiamen University, Xiamen, Fujian 361005, China
Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1, Hongo, Bunkyoku, Tokyo 113-0033, Japan; norita@astron.s.u-tokyo.ac.jp
Data
and
images
available
http://swxcs.ustc.edu.cn
at
http://www.arcetri.astro.it/SWXCS/
and
The Swift X-ray Telescope Cluster Survey III:
cluster catalog from 2005-2012 archival data
Teng Liu (刘腾)1 , Paolo Tozzi2 , Elena Tundo2, Alberto Moretti3, Piero Rosati4 , Jun-Xian Wang
(王俊贤)1 , Gianpiero Tagliaferri5 , Sergio Campana5 , Mauro Giavalisco6
ABSTRACT
We present the catalog of the Swift X-ray Cluster Survey (SWXCS) obtained using the archival data of the X-ray Telescope (XRT) onboard the Swift satellite acquired
from February 2005 to November 2012, extending the first release of the SWXCS. The
catalog provides positions, soft fluxes and, when possible, optical counterparts for a
flux-limited sample of X-ray group and cluster candidates. We consider the fields
with Galactic latitude |b| > 20◦ to avoid high HI column densities. We discard all
the observations targeted at groups or clusters of galaxies, as well as particular extragalactic fields not suitable to search for faint extended sources. We finally select
∼ 3000 useful fields covering a total solid angle of ∼ 400 deg2 . We identify extended
source candidates in the soft-band (0.5-2 keV) images of these fields, using the software EXSdetect, which is specifically calibrated on XRT data. Extensive simulations
are used to evaluate contamination and completeness as a function of the source signal, allowing us to minimize the number of spurious detections and to robustly assess
the selection function. Our catalog includes 263 candidate galaxy clusters and groups,
down to a flux limit of 7 × 10−15 erg cm−2 s−1 in the soft band, and the logN-logS is
in very good agreement with previous deep X-ray surveys. The final list of sources
1
CAS Key Laboratory for Research in Galaxies and Cosmology, Department of Astronomy, University of Science
and Technology of China, 230026, Hefei, Anhui, P.R. China; liuteng@ustc.edu.cn
2
INAF, Osservatorio Astrofisico di Firenze, Largo Enrico Fermi 5, I-50125, Firenze, Italy
3
INAF, Osservatorio Astronomico di Brera, Via Brera 28, I-20121 Milano, Italy
4
Università degli Studi di Ferrara, Dipartimento di Fisica e Scienze della Terra, Via Saragat 1 I-44121 Ferrara, Italy
5
INAF, Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807, Merate (LC), Italy
6
University of Massachusetts, Department of Astronomy, LGRT-B 619E, 710 North Pleasant Street, Amherst, MA
(USA)
Astronomy & Astrophysics manuscript no. N3198A_A2col
March 16, 2015
c
ESO
2015
The Dark Matter Distribution in the Spiral NGC 3198 out to 0.22 Rvir
E.V. Karukes1, 2 , P. Salucci1, 2 and G. Gentile3, 4
1
2
3
4
SISSA/ISAS, International School for Advanced Studies, Via Bonomea 265, 34136, Trieste, Italy
e-mail: ekarukes@sissa.it
INFN, Sezione di Trieste, Via Valerio 2, 34127, Trieste, Italy
Department of Physics and Astrophysics, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
Sterrenkundig Observatorium, Universiteit Gent, Krijgslaan 281, B-9000 Gent, Belgium
March 16, 2015
ABSTRACT
Aims. We use recent very extended (out to 48 kpc) HI kinematics alongside with previous Hα kinematics of the spiral galaxy NGC
3198 in order to derive its distribution of Dark Matter (DM).
Methods. First, we use a chi-square method to model the Rotation Curve of this galaxy in terms of different profiles of its DM
distribution: the Universal Rotation Curve (URC) mass model (stellar disk + Burkert halo + gaseous disk), the NFW mass model
(stellar disk + NFW halo + gaseus disk) and the BaryonΛCDM mass model (stellar disk + NFW halo modified by baryonic physics
+ gaseous disk). Secondly, in order to derive the DM halo density distribution we apply a new method developed by Salucci et al.
(2010) which does not require a global and often uncertain mass modelling.
Results. We find that, while, according to the standard method, both URC and NFW mass models can account for the RC, the new
method instead leads to a density profile which is in sharp disagreement with the dark halo density distribution predicted within the
Lambda Cold Dark Matter (ΛCDM) scenario. We find that the effects of baryonic physics proposed by Di Cintio et al. (2014) modify
the original ΛCDM halo densities in such a way that the resulting profile is more compatible with the DM density of NGC 3198
derived using our new method. However, at large distances, r ∼ 25 kpc, also this modified BaryonΛCDM halo profile appears in
tension with the derived DM halo density.
Key words. Dark Matter; Galaxy: NGC 3198; NFW halos; Universal Rotation Curve; Baryonic Feedback
1. Introduction
It has been known for several decades that the kinematics of disk
galaxies leads to a mass discrepancy (e.g. Bosma (1978); Bosma
& van der Kruit (1979); Rubin et al. (1980)). More precisely,
while in their inner regions, ranging between 1 and 3 disk exponential scale lengths according to the galaxy luminosity (Salucci
& Persic 1999), the observed stellar/baryonic matter accounts
for the Rotation Curves (RCs) (e.g. Athanassoula et al. (1987);
Persic & Salucci (1988); Palunas & Williams (2000)), in the
outer regions, we must add an extra mass component, namely
a Dark Matter (DM) halo in order to account for the latter. The
kinematics of spirals is now routinely interpreted in the framework of a DM component. In the widely accepted Lambda Cold
Dark Matter (ΛCDM) scenario the virialized structures are distributed according the well known NFW profile, proposed by
Navarro, Frenk and White (Navarro et al. 1996). ΛCDM scenario describes well the large-scale structure of the Universe
(e.g. Springel et al. (2006)), but it seems to fail on the scales
of galaxies (de Blok & Bosma 2002; Gentile et al. 2004, 2005).
In detail, the NFW density profile leads to the ”core-cusp problem”: empirical profiles with a central core of constant density,
such as the pseudo-isothermal (Begeman et al. 1991; Kent 1986),
and the Burkert (Salucci & Burkert 2000) fit the available RCs
much better than the mass models based on NFW halos.
In the present paper, we derive the DM content and distribution in the spiral galaxy NGC 3198. This galaxy has been subject of several investigations: it was studied by means of optical
(Cheriguène 1975; Hunter et al. 1986; Bottema 1988; Wevers
et al. 1986; Kent 1987; Corradi et al. 1991; Daigle et al. 2006)
and HI-21 cm radio observations (Bosma (1981); van Albada
et al. (1985); Begeman (1987) established it as the object with
the clearest evidence for dark matter (see also de Blok et al.
(2008); Gentile (2008))).
Our present analysis is based, mainly, on the HI observations
by Gentile et al. (2013), part of the HALOGAS (Westerbork Hydrogen Accretion in LOcal GAlaxieS) survey. The main goal of
HALOGAS is to investigate the amount and properties of extraplanar gas by using very deep HI observations. In fact, for this
galaxy, they presented a very extended RC out to 720 arcsec, corresponding to ∼ 48 kpc for a galaxy distance at 13.8 Mpc (Freedman et al. 2001). Notice, that the previous HI observations by de
Blok et al. (2008) were extended only out to ∼ 38 kpc, for the
same galaxy distance. In Gentile et al. (2013) this extended RC
was modelled in the framework of Modified Newtonian dynamics (MOND). Here, we want to use such an uniquely extended
kinematics to help resolving the Dark Matter core/cusp issue.
In detail, we will apply to the very reliable kinematics available
from 2 to 48 kpc two different mass decomposition methods that
will derive the DM halo structure. This will be compared with
a) the empirically based halo profiles coming from the Universal Rotation Curve, b) the NFW halos and c) the BaryonΛCDM
halos, the outcome of scenarios in which baryonic physics has
shaped the DM halo density.
This paper is organized as follows. In Sec. 2 we present the
HI and Hα kinematics used in this study. In Sec.3 we model the
RC by using the quadrature sum of the contributions of the individual mass components (stellar disk + dark halo + gas disk)
Influence from cosmological uncertainties on galaxy number count at faint limit
Keji Shen1 , Qiang Zhang1 , and Xin-he Meng1,2∗
1
Department of Physics,
Nankai University, Tianjin 300071, China.
and
2
State Key Laboratory of Theoretical Physics,
Institute of Theoretical Physics,
Chinese Academic of Science, Beijing 100190, China.
Counting galaxy number density with wide range sky surveys has been well adopted in researches
focusing on revealing evolution pattern of different types of galaxies. As understood intuitively
the astrophysics environment physics is intimated affected by cosmology priors with theoretical
estimation or vise versa, or simply stating that the astrophysics effect couples the corresponding
cosmology observations or the way backwards. In this article we try to quantify the influence on
galaxy number density prediction at faint luminosity limit from the uncertainties in cosmology, and
how much the uncertainties blur the detection of galaxy evolution, with the hope that this trying
may indeed help for precise and physical cosmology study in near future or vise versa.
I.
INTRODUCTION
Galaxy number count measures the number density n of galaxies per unit solid angle
dω at redshift z within the luminosity range
[L, L + dL] as [1, 11]
n (ˆ
r , L, z) dL dz dω = φ (L, z) dL dVˆ ,
(1)
where φ(L, z) is the luminosity function (LF for
short); rˆ represents a specific direction on comoving coordinate with the corresponding differential volume dVˆ . The anisotropic metric is
encoded in the direction, while for isotropic and
homogeneous FRW metric, the relation between
number density and LF is much simpler by integration over the solid angle and gives
DL2
n (L, z) dL dz = φ(L, z)
dL dz,
(1 + z)5 h3 E
(2)
where E, the dimensionless Hubble parameter at
redshift z equals to H/(100h km · s−1 · Mpc−1 )
and the luminosity distance is defined as dL =
c
D . The dimensional constant parameters are
H0 L
absorbed by normalization factor in luminosity
function, leaving dimensionless terms. The luminosity functions are usually measured in the
non-parametric way by astrophysicist, but that
∗ Electronic
address: xhm@nankai.edu.cn
approach is based on pre-selected fiducial modeling of background cosmological evolution. It is
believed that variations in cosmological parameters are too weak to be captured through the
noisy observation, but we are driven by the optimism that sooner or later we are able to detect
them.
II.
THEORETICAL FRAMEWORK
Luminosity function contains the intrinsic
characteristic of different sets of galaxies, usually affected by redshifts, galaxy types and local environments. According to the assumption
of the hierarchical structure formation with cold
dark matter model, the most adopted analytical parameterization of luminosity function is
the Schechter form [2] which reads
φ(L)dL =
φ∗ L α
L
( ∗ ) exp(− ∗ )dL,
∗
L L
L
(3)
with L∗ , the characteristic luminosity and α, the
faint-end slope parameter. Other well-known
luminosity function forms are for example, the
power-law model [3]:
φ(L)dL = φ∗ L1−η (1 +
L −β
) dL,
βL∗
(4)
5th Fermi Symposium : Nagoya, Japan : 20-24 Oct, 2014
Kanata optical and X-ray monitoring of Gamma-ray emitting
Narrow-Line Seyfert 1 and Radio galaxies
K. Kawaguchi, Y. Fukazawa, R. Itoh, Y. Kanda, K. Shiki, K. Takaki
Department of Physical Science, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
Y.T. Tanaka, M. Uemura, H.Akitaya
Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526,
Japan
Broadband spectrum of AGN consists of multiple components such as jet emission and accretion disk emission.
Temporal correlation study is useful to understand emission components and their physical origins. We have
performed optical monitoring using Kanata telescope for 4 radio galaxies and 6 radio-loud Narrow-Line Seyfert
1 (RL-NLSy1): 2 gamma-ray-loud RL-NLSy1s, 1H 0323+342 and PMN J0948+0022, and 4 gamma-ray-quiet
RL-NLSy1s. From these results, it is suggested that RL-NLSy1s show a disk-dominant phase and a jet-dominant
phase in the optical band, but it is not well correlated with brightness.
1. Introduction
Active Galactic Nucleus (AGNs) emit electromagnetic radiation from radio up to TeV gamma-ray
ranges. Spectral Energy Distribution (SED) of blazars
is often dominanted by 2 component, synchrotron
emission and Inverse Compton from a relativistic
jet. However, SED of misaligned radio-loud AGNs
is complicated due to disk/corona emission. In
addition to the above two components, we can see
disk emission from near-infrared to ultraviolet bands
and corona emission in X-ray band. Because it
is difficult to separate these components, optical
emission mechanism is still unclear.
Radio galaxy is radio-loud AGN which has a relative
large viewing angle. Thanks to high sensitive observation by Fermi Gamma-Ray Space Telescope/ Large
Area Telescope (LAT), correlation study between
optical and MeV/GeV gamma-ray bands has become
available, but correlation between optical and X-ray
bands is still unclear.
Narrow-Line Seyfert 1(NLSy1) is a subclass of Seyfert
1 galaxies. Most of NLSy1 is radio-quiet, but a few
objects( 7%) are radio-loud. Recently, Fermi-LAT
detected MeV/GeV gamma-ray emission from radioloud NLSy1 (RL-NLSy1) and now RL-NLSy1 is a
new class of gamma-ray emitting AGNs. Radioloud NLSy1 shows fast and strong variability like
blazars. The most gamma-ray bright NLSy1 PMN
J0948+0022 showed minute-scale optical variability,
correlated with polarization degree[4]. This indicates
that synchrotron emision from the jet is dominant
in the optical band, but other study shows disk
emission is also dominant in the optical band[1].
Hence emission mechanism in the optical band in
RL-NLSy1 is still unclear.
eConf C141020.1
Table I Target lists
Radio galaxies
3C 111
3C 120
3C 390.3
NGC 1275
Gamma-ray loud NLSy1s
PMN J0948+0022
1H 0323+342
Gamma-ray quiet NLSy1s
FBQS J1629+4007 FBQS J1644+2619
SDSS J1722+5654 SDSS J1450+5919
2. Observation
We have performed optical monitor with the
Kanata optical telescope. We use MAXI, Swift-BAT
and Fermi-LAT public data for X-ray and gamma-ray
monitor.
We selected famous and X-ray bright objects for radio galaxies. For RL-NLSy1, we selected gammaray loud objects and a few gamma-ray quiet objects.
These gamma-ray quiet objects are reported to have
a blazar-like radio structure and high brightness temperature by Komossa et al. (2006)[2] Doi et al.
(2011)[6] and Doi et al. (2012)[7]. So if these gammaray quiet NLSy1 has a relativistic jet, flares in the
optical band are expected.
3. Results
Radio galaxies
Fig 1–4 show the results for radio galaxies. Each figure
show optical R-band(top), V-band(second) magnitude
by Kanata, 2-20 keV daily X-ray count rate by MAXI
(third), and 15-150 keV weekly count rate by SwiftBAT (bottom). The gaps in MAXI light curves are
the period when objects are not in FOV of MAXI.
There is no Swift-BAT public data for 3C 390.3. We
1
Astronomy & Astrophysics manuscript no. aa_ACHer_arXiv
March 16, 2015
c
ESO
2015
The evolved circumbinary disk of AC Her: a radiative transfer,
interferometric and mineralogical study ?
M. Hillen1 , B.L. de Vries2, 3 , J. Menu1 , H. Van Winckel1 , M. Min4 , and G. D. Mulders5
1
2
3
4
5
Instituut voor Sterrenkunde (IvS), KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
e-mail: Michel.Hillen@ster.kuleuven.be
AlbaNova University Centre, Stockholm University, Department of Astronomy, SE-106 91, Stockholm, Sweden
Stockholm University Astrobiology Centre, SE-106 91 Stockholm, Sweden
Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
Lunar and Planetary Laboratory, The University of Arizona, 1629 E. University Blvd., Tucson AZ 85721, USA
Received 19 November, 2014; accepted 11 March, 2015
ABSTRACT
Context. Many post-asymptotic giant branch (post-AGB) stars in binary systems have an infrared (IR) excess arising from a dusty
circumbinary disk. The disk formation, current structure, and further evolution are, however, poorly understood.
Aims. We aim to constrain the structure of the circumstellar material around the post-AGB binary and RV Tauri pulsator AC Her. We
want to constrain the spatial distribution of the amorphous as well as of the crystalline dust.
Methods. We present very high-quality mid-IR interferometric data that were obtained with the MIDI/VLTI instrument. We analyse
the MIDI visibilities and differential phases in combination with the full SED, using the MCMax radiative transfer code, to find a good
structure model of AC Her’s circumbinary disk. We include a grain size distribution and midplane settling of dust self-consistently in
our models. The spatial distribution of crystalline forsterite in the disk is investigated with the mid-IR features, the 69 µm band and
the 11.3 µm signatures in the interferometric data.
Results. All the data are well fitted by our best model. The inclination and position angle of the disk are well determined at i = 50 ± 8◦
and PA = 305 ± 10◦ . We firmly establish that the inner disk radius is about an order of magnitude larger than the dust sublimation
radius. The best-fit dust grain size distribution shows that significant grain growth has occurred, with a significant amount of mmsized grains now being settled to the midplane of the disk. A large total dust mass ≥ 10−3 M is needed to fit the sub-mm fluxes.
By assuming αturb = 0.01, a good fit is obtained with a small grain size power law index of 3.25, combined with a small gas/dust
ratio ≤10. The resulting gas mass is compatible with recent estimates employing direct gas diagnostics. The spatial distribution of the
forsterite is different from the amorphous dust, as more warm forsterite is needed in the surface layers of the inner disk.
Conclusions. The disk in the AC Her system is in a very evolved state, with its small gas/dust ratio and large inner hole. Mid-IR
interferometry offers unique constraints, complementary to mid-IR features, for studying the mineralogy in disks. A better uv coverage
is needed to constrain in detail the distribution of the crystalline forsterite in the disk of AC Her, but we find strong similarities with
the protoplanetary disk HD100546.
Key words. Stars: AGB and post-AGB – Stars: circumstellar matter – Stars: binaries: general – Techniques: photometric – Tech-
niques: interferometric – Infrared: stars
1. Introduction
Post-Asymptotic Giant Branch stars (post-AGB stars) are an
evolved evolutionary phase of low- to intermediate mass stars.
They show a large variety in circumstellar characteristics (van
Winckel 2003), but a significant fraction of the optically-bright
objects show a distinctive near-IR excess (de Ruyter et al. 2006;
Kamath et al. 2014). This excess can be explained as due to
thermal emission of warm dust in the close environment of the
central source (de Ruyter et al. 2006). It is now well established that this SED characteristic indicates the presence of a
stable and compact dusty reservoir, likely a Keplerian disk (e.g.
de Ruyter et al. 2006; Deroo et al. 2007a; Hillen et al. 2013,
2014). This was confirmed when the Keplerian rotation of the
gas was first resolved by Bujarrabal et al. (2005) in one object, and recently endorsed by the most detailed position-velocity
maps of the same object with the Atacama Large Millimeter Ar?
Based on observations made with ESO Telescopes at the La Silla
Paranal Observatory under program ID 075.D-0605.
ray (ALMA) by Bujarrabal et al. (2013b). A survey using singledish CO line data confirms that rotation is widespread (Bujarrabal et al. 2013a), which is a strong observational indicator of
stability. While the formation nor the evolution of these disks is
well understood, both are linked to binary interaction processes,
as evidence is mounting that sources with disk-like SEDs are indeed all binaries (van Winckel et al. 2009; Gorlova et al. 2013).
The longevity of the disk is further corroborated by the
strong processing of the dust grains as attested by the infrared
spectral dust-emission features (e.g. Gielen et al. 2008, 2011)
and the mm continuum fluxes that indicate the presence of large
grains (de Ruyter et al. 2005). A striking result is the large abundance and almost ubiquitous presence of crystalline grains (Molster et al. 2002b; Gielen et al. 2011).
Crystalline olivine grains ((Mg,Fe)2 SiO4 ) are formed by
high temperature (>1000 K) processes, either condensation from
the gas phase or annealing of amorphous dust grains. This makes
crystalline dust a tracer of high temperature regions and processes in the disk. In protoplanetary disks crystalline dust is
Hα and EUV observations of a partial CME
Damian J. Christian
Department of Physics and Astronomy, California State University Northridge, 18111
Nordhoff Street, Northridge, CA 91330, USA; daman.christian@csun.edu
David B. Jess
Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University
Belfast, Belfast, BT7 1NN, Northern Ireland, U.K.
Patrick Antolin
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588,
Japan
Mihalis Mathioudakis
Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University
Belfast, Belfast, BT7 1NN, Northern Ireland, U.K.
;
Received
accepted
–2–
ABSTRACT
We have obtained Hα high spatial and time resolution observations of the
upper solar chromosphere and supplemented these with multi-wavelength observations from the Solar Dynamic Observatory (SDO) and the Hinode ExtremeUltraviolet Imaging Spectrometer (EIS). The Hα observations were conducted on
11 February 2012 with the Hydrogen-Alpha Rapid Dynamics Camera (HARDcam) instrument at the National Solar Observatory’s Dunn Solar Telescope. Our
Hα observations found large downflows of chromospheric material returning from
coronal heights following a failed prominence eruption. We have detected several
large condensations (“blobs”) returning to the solar surface at velocities of ≈200
km s−1 in both Hα and several SDO AIA band passes. The average derived
size of these “blobs” in Hα is 500 by 3000 km2 in the directions perpendicular
and parallel to the direction of travel, respectively. A comparison of our “blob”
widths to those found from coronal rain, indicate there are additional smaller,
unresolved “blobs” in agreement with previous studies and recent numerical simulations. Our observed velocities and decelerations of the “blobs” in both Hα
and SDO bands are less than those expected for gravitational free-fall and imply
additional magnetic or gas pressure impeding the flow. We derived a kinetic
energy ≈2 orders of magnitude lower for the main eruption than a typical CME,
which may explain its partial nature.
Subject headings: Sun:chromosphere – Sun: corona – Sun: filaments,
prominences
The effects of binary interactions on parameter determinations for
early-type galaxies
Yu
Zhang1? , Jinzhong Liu1 , Fenghui Zhang2
1
Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi 830011, China
Observatory, Chinese Academy of Sciences, Kunming 650011, China
2 Yunnan
16 March 2015
ABSTRACT
Based on stellar population models without (SSP) and with (BSP) binary interactions, we investigate the effects of binary interactions on parameter determinations for early-type galaxies
(ETGs). We present photometric redshift (photo-z), age and spectral type for photometric data
sample by fitting observed magnitudes with the SSP and BSP models. Our results show that
binary interactions have no effect on photo-z estimation. Once we neglect binary interactions,
the age of ETGs will be underestimated, by contrast, the effects on the age estimations can
be negligible for other type of galaxies. For ETG sample, we derive their properties by fitting their spectra with the SSP and BSP models. When comparing these galaxy properties,
we find no variation of the overall metallicities for ETGs among the SSP and BSP models.
Moreover, the inclusion of binary interactions can affect age estimations. Our results show
that the BSP-fitted ages in ∼ 33.3% of ETG sample are around 0.5 − 1.0 Gyr larger than the
SSP-fitted ages; ∼ 44.2% are only 0.1 − 0.5 Gyr larger; the rest ∼ 22.5% are approximately
equal. By comparisons, we find the difference of the star formation rate between the SSP and
BSP models is large at the late evolution stage.
Key words: binaries: general – galaxies: fundamental parameters – galaxies: stellar content
1
INTRODUCTION
Early-type galaxies (ETGs), which comprise elliptical and lenticular (S0) galaxies, are the oldest class of galaxy. And their stellar populations formed at early time (Trager et al. 2000; Temi
et al. 2005; De Lucia et al. 2006) and passively evolved to
their present styles. The phenomenon of far-ultraviolet (FUV) excess in ETGs became surprising since its first discovery by the
Orbitting Astronomical Observatory − 2 in 1969 (Code et al.
1972; Burstein et al. 1988). The flux in the spectral energy distributions (SEDs) of ETGs increases with a decreasing wavelength
˚ This behavior is known as UV
in the range from 2000 to 1200A.
upturn, UV rising-branch, or UVX (see O’Connell 1999, for a review). And some recent studies show evidence that ETGs have
some current events of minor star formation (Kaviraj et al. 2007;
Schawinski et al. 2007; Salim et al. 2012; Barway et al. 2013),
which contribute the FUV spectra.
The favored origin of the UV-upturn is extreme horizontal
branch (EHB) stars and their descendants, either metal poor (Lee
1994; Park & Lee 1997) or metal rich (Bressan et al. 1994; Yi et al.
1997). And the detection of EHB stars in the dwarf elliptical galaxy
M32 provide direct evidence for the EHB origin of the UV-upturn.
Meanwhile, binary evolution can also reproduce EHB stars (Han
et al. 2002, 2003). Han et al. (2007) have used three possible bi-
?
E-mail: zhy@xao.ac.cn
nary evolution channels for EHB stars to explain the UV-upturn in
ETGs, with limited dependence on age and metallicity. HernándezPérez & Bruzual (2014) also used the stellar population model with
binary stars to study the UV-upturn of ETGs, and found that the
UV-upturn was very sensitive to the fraction of binary stars.
Binary stars are very common in galaxies, and the evolution of
binary stars is different from that of single stars. Meanwhile, observations also show that binary stars are common in nearby star clusters and galaxies (Abt 1983; Carney et al. 2005; Sollima et al. 2007;
Raghavan et al. 2010; Minor 2013). Brinchmann (2010) also indicated that the importance of binary stars was one of six important
challenges in stellar population studies in the next decades. However, only few works had done for studying the influence of binary
evolution on stellar population properties. Zhang et al. (2004, 2005)
have shown that the UV passbands could be about 2.0 − 3.0 mag
enhanced once binary interactions have been taken into account.
Therefore, ignoring the binary interactions in evolution population
synthesis (EPS) models can underestimate the UV flux and affect
the property determinations for stellar population systems (Zhang
et al. 2012a,b, 2013)
While the importance of binary evolution has been shown, detailed studies of the effects of binary stars on property determinations of ETGs are not enough. Therefore, we investigate the effects
of binary interactions on parameter determinations for ETGs based
on the EPS models with and without binary interactions. At the
first step, we use a standard SED fitting procedure to fit the SED
Testing subhalo abundance matching from redshift-space clustering
Mikito Yamamoto,1 Shogo Masaki2 and Chiaki Hikage3
1
2
3
Department of Physics, Nagoya University, Aichi 464-8602, Japan
NTT Secure Platform Laboratories, NTT Corporation, Tokyo 180-8585, Japan
Kobayashi Maskawa Institute (KMI), Nagoya University, Aichi 464-8602, Japan
16 March 2015
ABSTRACT
We present a first application of the subhalo abundance matching (SHAM) method to describe
the redshift-space clustering of galaxies including the non-linear redshift-space distortion, i.e.,
the Fingers-of-God. We find that the standard SHAM connecting the luminosity of galaxies
to the maximum circular velocity of subhalos well reproduces the luminosity dependence of
redshift-space clustering of galaxies in the Sloan Digital Sky Survey in a wide range of scales
from 0.3 to 40 h−1 Mpc. The result indicates that the SHAM approach is very promising
for establishing a theoretical model of redshift-space galaxy clustering without additional
parameters. We also test color abundance matching using two different proxies for colors:
subhalo age and local dark matter density following the method by Masaki et al. (2013b).
Observed clustering of red galaxies exhibits much stronger Fingers-of-God effect than blue
galaxies. We find that the subhalo age model describes the observed color-dependent redshiftspace clustering much better than the local dark matter density model. The result infers that
the age of subhalos is a key ingredient to determine the color of galaxies.
Key words: galaxies: formation – galaxies: haloes – galaxies: statistics cosmology: observations – cosmology: large-scale structure of Universe
1 INTRODUCTION
Establishing connection between the properties of galaxies and the
underlying dark matter is crucial for both studies of galaxy evolution and cosmology. Star formation histories of galaxies has been
studied by associating galaxies with their host dark matter halos
and their connection provides fundamental constraints on galaxy
formation models (e.g., Conroy & Wechsler 2009; Leauthaud et al.
2010; Behroozi et al. 2013). Future galaxy surveys such as Prime
Focus Spectrograph (PFS) (Takada et al. 2012), the Dark Energy
Spectroscopic Instrument (DESI) (Levi et al. 2013), Euclid (Laureijs et al. 2011) and the Wide Field Infrared Survey Telescope
(WFIRST) (Spergel et al. 2013) use both luminous red galaxies and
<
emission line galaxies to trace the large-scale structure at z ∼
2. A
major uncertainty for the precision cosmology using galaxy surveys
comes from the challenge of relating galaxies and dark matter.
Subhalo abundance matching (SHAM) is a promising approach to relate the properties of galaxies to dark matter subhalos
(e.g., Kravtsov et al. 2004; Nagai & Kravtsov 2005; Conroy et al.
2006). The simple abundance matching model by assigning luminosity in the order of the maximum circular velocity of dark matter
subhalos successfully reproduces the galaxy clustering at different
redshifts (Conroy et al. 2006). Masaki et al. (2013a) also finds a
good abundance matching between the progenitor halos of luminous red galaxies (LRGs) and the massive halos at z ∼ 2 and then
explains the clustering properties of LRGs very well. There also has
been recent attempts to relate the galaxy color to the subhalo propc 0000 RAS
erties, i.e., color abundance matching. Galaxy color reflects the activity of on-going star formation: red galaxies consists of aged stars
and the star formation is quenched, whereas blue galaxies are relatively young and their star formation is active. It is also known that
redder galaxies live in denser environments via the measurement of
galaxy clustering (Norberg et al. 2002; Zehavi et al. 2005; Coil et al.
2008; Guo et al. 2014; Skibba et al. 2014) and also from the colordensity relation (Balogh et al. 2004; Cooper et al. 2006; Blanton
& Berlind 2007; Bamford et al. 2009). Masaki et al. (2013b) extends a SHAM technique to explain color-dependent properties of
galaxy clustering as well as galaxy-galaxy lensing using two proxies of color: one is the local dark matter density motivated by the
environmental dependence of galaxy color; the other is the subhalo
age reflecting the different aged population between red and blue
galaxies. Hearin & Watson (2013) also perform color abundance
matching by assigning the redshift zstarve characterizing the epoch
of star formation quenching to subhalos.
So far, the projected correlation function along the line-ofsight has been commonly used for testing SHAM to avoid the effect of redshift-space distortion (RSD) due to peculiar motion of
galaxies. The velocity of galaxies within and outskirts of clusters
is complicated and affected by different physics including the dynamical friction, tidal stripping/disruption, merging, and ram pressure. The internal motion of galaxies elongate the RSD of galaxies
along the line-of-sight direction, known as Fingers-of-God (FoG;
Jackson 1972). The FoG effect is clearly different by colors: red
galaxies show much stronger FoG effect than blue galaxies (Zehavi
Multi-wavelength Emission from the Fermi Bubble III. Stochastic
(Fermi) Re-Acceleration of Relativistic Electrons Emitted by
SNRs.
K. S. Cheng1 , D. O. Chernyshov1,2 , V. A. Dogiel1,2,3 , and C. M. Ko4
1
2
Department of Physics, University of Hong Kong, Pokfulam Road, Hong Kong, China
I.E.Tamm Theoretical Physics Division of P.N.Lebedev Institute of Physics, Leninskii pr.
53, 119991 Moscow, Russia
3
Moscow Institute of Physics and Technology (State University), 9, Institutsky lane,
Dolgoprudny, 141707, Russia
4
Institute of Astronomy, Department of Physics and Center for Complex Systems, National
Central University, Jhongli, Taiwan
March 16, 2015
Received
0
;
accepted
........
–2–
ABSTRACT
We analyse the model of stochastic re-acceleration of electrons, which are
emitted by supernova remnants (SNRs) in the Galactic Disk and propagate then
into the Galactic halo, in order to explain the origin on nonthermal (radio and
gamma-ray) emission from the Fermi Bubbles (FB). We assume that the energy
for re-acceleration in the halo is supplied by shocks generated by processes of star
accretion onto the central black hole. Numerical simulations show that regions
with strong turbulence (places for electron re-acceleration) are located high up in
the Galactic Halo about several kpc above the disk. The energy of SNR electrons
that reach these regions does not exceed several GeV because of synchrotron and
inverse Compton energy losses. At appropriate parameters of re-acceleration
these electrons can be re-accelerated up to the energy 1012 eV which explains in
this model the origin of the observed radio and gamma-ray emission from the
FB. However although the model gamma-ray spectrum is consistent with the
Fermi results, the model radio spectrum is steeper than the observed by WMAP
and Planck. If adiabatic losses due to plasma outflow from the Galactic central
regions are taken into account, then the re-acceleration model nicely reproduces
the Planck datapoints.
1.
Introduction
Recently Fermi has discovered two giant gamma-ray Bubbles (FBs) that extend
nearly 10 kpc in diameter north and south of the Galactic center (cf. Dobler et al. 2010;
Su et al. 2010, for more recent analyses, see Hooper & Slatyer (2013); Yang et al., (2014);
Ackermann et al. (2014)). These gamma-ray Bubbles also correlate with the earlier
CHINESE
ASTRONOMY
AND ASTROPHYSICS
Chinese Astronomy and Astrophysics 000 (2014) 0–2
Quark-Hadron Phase Transition
with Finite-Size Effects in Neutron Stars†
N. Yasutake△,1 , S. Benic2 , D. Blaschke3 , T. Maruyama4 , T. Tastumi5
1. Physics Department, Chiba Institute of Technology,
Shibazono 2-1-1, Narashino, Chiba, 275-0023, Japan
2. Physics Department, Faculty of Science, University of Zagreb, Zagreb 10000, Croatia
3. Institute for Theoretical Physics, University of Wroclaw,
Max Born pl. 9, 50-204 Wroclaw, Poland
4. Advanced Science Research Center, Japan Atomic Energy Agency,
Tokai, Ibaraki 319-1195, Japan
5. Department of Physics, Kyoto University, Kyoto 606-8502, Japan
Abstract
We study the quark-hadron phase transition with the finite-size
effects in neutron stars. The finite-size effects should be, generally, taken into
account in the phase transition of multi-component system. The behavior of
the phase transition, however, strongly depends on the quark model, hadron
model, surface tension, neutrino fraction, and temperature. We find that, if
the surface tension is strong, the EOS becomes to be close the one with the
Maxwell condition for any hadron and/or quark models, though we adopt the
Gibbs conditions. We also find that the mass-radius relations by the EOS are
consistent with the observations, and our model is, then, applicable to realistic
astrophysical phenomena such as the thermal evolutions of compact stars.
Key words
equation of state—stars: neutron stars, magnetars
1.
INTRODUCTION
The equation of state (EOS) is one of the most important topic to study on neutron stars.
But there is large uncertainty at finite-density region in the EOS. One of the possibility
for understanding the EOS of neutron stars (NSs) is to study baryon-baryon(BB) interactions by Lattice QCD (LQCD) simulations [1] and/or experiments such as heavy-ion
†
This work was supported by JSPS KAKENHI Grant Numbers 25105510, 23540325, 24105008.
△
nobutoshi.yasutake@p.chibakoudai.jp
c 2011 Elsevier Science B. V. All rights reserved.
0275-1062/01/$-see front matter PII:
DRAFT: March 16, 2015
INVESTIGATING Hα, UV, AND IR STAR-FORMATION RATE DIAGNOSTICS FOR A LARGE SAMPLE OF
z ∼ 2 GALAXIES
Irene Shivaei1,2, Naveen A. Reddy1,3 , Charles C. Steidel4 , Alice E. Shapley5
DRAFT: March 16, 2015
ABSTRACT
We use a sample of 262 spectroscopically confirmed star-forming galaxies at redshifts 2.08 ≤ z ≤ 2.51
to compare Hα, UV, and IR star-formation-rate diagnostics and to investigate the dust properties of
the galaxies. At these redshifts, the Hα line shifts to the Ks -band. By comparing Ks -band photometry
to underlying stellar population model fits to other UV, optical, and near-infrared data, we infer the Hα
flux for each galaxy. We obtain the best agreement between Hα- and UV-based SFRs if we assume
that the ionized gas and stellar continuum are reddened by the same value and that the Calzetti
attenuation curve is applied to both. Aided with MIPS 24 µm data, we find that an attenuation
curve steeper than the Calzetti curve is needed to reproduce the observed IR/UV ratios of galaxies
younger than 100 Myr. Furthermore, using the bolometric star-formation rate inferred from the UV
and mid-IR data (SFRIR +SFRUV ), we calculated the conversion between the Hα luminosity and SFR
to be (7.5 ± 1.3) × 10−42 for a Salpeter IMF, which is consistent with the Kennicutt (1998) conversion.
The derived conversion factor is independent of any assumption of the dust correction and is robust
to stellar population model uncertainties.
Subject headings: galaxies: evolution — galaxies: high-redshift – galaxies: star formation
1. INTRODUCTION
One of the most important diagnostics in understanding the evolution of galaxies is the star-formation rate
(SFR). The evolution of the SFR of galaxies can give
clues as to how galaxies were enriched with heavy elements, how they build up their stellar mass through
cosmic time, and helps us to understand the bolometric output of galaxies. At redshift z ∼ 2, when the
universe was just ∼ 3 Gyr old, star-formation activity
in the universe was at its peak and galaxies were in
the process of assembling most of their stellar mass
(see Reddy & Steidel 2009; Bouwens et al. 2010; Shapley
2011; Madau & Dickinson 2014). Studying this critical
epoch is essential to gaining a better understanding of
the evolution of the progenitors of the local galaxy population.
The ultra-violet (UV) continuum (1500 to 2800 ˚
A ) intensity of a galaxy is one of the most commonly used
diagnostics for the SFR as it is observable over a wide
range of redshifts and intrinsic luminosities. It is sensitive to massive stars (M∗ & 5 M⊙ ), making it a direct
tracer of current SFR. By extrapolating the formation
rate of massive stars to lower masses, for an assumed
form of the initial mass function (IMF), one can estimate
the total SFR (Madau et al. 1998). Another widely used
diagnostic for measuring the SFR is nebular emission,
with Hα being the most common because of its higher
1 Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521,
USA
2 NSF Graduate Research Fellow
3 Alfred P. Sloan Research Fellow
4 Cahill Center for Astronomy and Astrophysics, California
Institute of Technology, 1216 E. California Blvd., MS 249-17,
Pasadena, CA 91125, USA
5 Department of Physics & Astronomy, University of California, Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095,
USA
intensity compared to the other hydrogen recombination
lines such as Hβ, Paα, Paβ, etc., and it is easier to interpret than the Lyα line. Hα is an “instantaneous” tracer
of SFR because it is sensitive only to the most massive
stars (M∗ & 10 M⊙ ). However, it becomes more challenging to observe Hα from the ground at z & 1 because
the line is redshifted to the near-IR where the terrestrial
background is much higher than at optical wavelengths.
The main disadvantage of using UV/optical luminosities as tracers of the SFR is their sensitivity to dust attenuation. The dust absorption cross-section is larger for
shorter wavelengths and choosing the appropriate attenuation curve to correct the observed luminosities plays an
important role in determining intrinsic physical quantities. Aside from the assumed attenuation curve, the geometry of dust with respect to the stars can lead to different color excesses, E(B−V ), between the ionized gas and
the stellar continuum. E(B − V ) is the color excess measured between the B and V bands, E(B −V ) ≡ AB −AV ,
where Aλ is the total extinction at wavelength λ in magnitudes. In particular, the nebular recombination lines
arise from the HII regions around the most massive O
and early-type B stars (with masses of M∗ & 10 M⊙
and main sequence lifetimes of . 10 Myr). On the other
hand, for a Salpeter IMF, solar metallicity, and a constant or rising star-formation history, the UV continuum
in starburst galaxies originates from stars over a broader
range of mass that includes later-type B stars with lifetimes . 100 Myr (Kennicutt 1998; Madau & Dickinson
2014). These older non-ionizing stars have more time to
migrate to regions of lower dust density in the galaxy,
while H-ionizing stars with shorter lifetimes do not have
enough time to escape from their dusty birthplace or let
the parent molecular clouds to dissipate. As a result,
the nebular lines can be subject to a higher degree of
reddening than the UV continuum.
Calzetti et al. (1994) found that the nebular emission
Rhapsody-G simulations: Galaxy clusters as baryonic closed
boxes and the covariance between hot gas and galaxies
Hao-Yi Wu,1 ? August E. Evrard,1 Oliver Hahn,2 Davide Martizzi,3
Romain
Teyssier,4 Risa H. Wechsler5
1
Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA
Department of Physics, ETH Zurich, CH-8093 Z¨
urich, Switzerland
3 Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
4 Institute for Computational Science, University of Zurich, CH-8057 Z¨
urich, Switzerland
5 KIPAC, Physics Department, Stanford University, Stanford, CA 94305, USA and
SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA
2
16 March 2015
ABSTRACT
Within a sufficiently large cosmic volume, conservation of baryons implies a simple “closed
box” view in which the sum of the baryonic components must equal a constant fraction of
the total enclosed mass. We present evidence from Rhapsody-G hydrodynamic simulations
of massive galaxy clusters that the closed-box expectation may hold to a surprising degree
within the interior, non-linear regions of very massive haloes. We find a significant anticorrelation between hot gas mass fraction and galaxy mass fraction (cold gas + stars), with
rank correlation coefficient, −0.69, within R500c . Because of this anti-correlation, the total
baryon mass serves as a low-scatter proxy for total cluster mass. The fractional scatter in
total baryon fraction scales approximately as 0.02(∆c /100)0.6 , while the scatter of either
gas mass or stellar mass is larger in magnitude and declines more slowly with increasing
radius. We discuss potential observational tests using cluster samples selected by optical
and hot gas properties; the simulations suggest that joint selection on stellar and hot gas
has potential to achieve 5% scatter in total halo mass.
Key words: methods: numerical — galaxies: clusters: general — cosmology: theory —
X-rays: galaxies: clusters
1
INTRODUCTION
The abundance of galaxy clusters as a function of cluster mass
is sensitive to both the growth of structure and cosmic expansion, providing not only stringent constraints on cosmological
parameters but also consistency checks for the theory of gravity
(see, e.g., Miller et al. 2001; Vikhlinin et al. 2009; Mantz et al.
2010; Rozo et al. 2010; Rapetti et al. 2013; Benson et al. 2013;
and Allen et al. 2011 for a review). In cluster cosmology, the
key is to accurately infer the mass of galaxy clusters from their
observable properties, including gas mass and temperature
from X-ray emission (e.g., Mantz et al. 2014), galaxy content
from imaging and galaxy dynamics from spectroscopy (e.g.,
Kravtsov et al. 2014; Mamon et al. 2013), and strong and weak
gravitational lensing effects (e.g., von der Linden et al. 2014).
Each of these mass proxies exhibit a certain amount of scatter
around the true mass, and minimizing and characterizing this
scatter is essential for precision cosmology from galaxy cluster
surveys (e.g., Lima & Hu 2005; Wu et al. 2010).
?
Current address: California Institute of Technology, MC 367-17,
Pasadena, CA 91125, USA. E-mail: hywu@caltech.edu
c 0000 RAS
To achieve accurate mass measurements, multi-wavelength
observations have often been conducted for the same sample of
clusters; for example, the CLASH project includes comparison
between mass proxies from weak lensing, X-ray, and velocity
dispersion (Postman et al. 2012; Donahue et al. 2014; Biviano
et al. 2013); clusters observed by the South Pole Telescope
using the Sunyaev-Zeldovich effect have been followed up photometrically and spectroscopically (Song et al. 2012; Ruel et al.
2014). When multiple mass tracers are available for the same
sample of galaxy clusters, a joint selection can reduce the mass
scatter. In particular, the reduction of mass scatter is most
effective when the two mass tracers are anti-correlated with
each other at a given mass (e.g., Cunha 2009; Stanek et al.
2010; Rozo et al. 2014; Evrard et al. 2014).
Hydrodynamical simulations of galaxy clusters have been a
powerful tool for understanding mass proxies (e.g., Evrard et al.
1996; Kravtsov et al. 2006; Rasia et al. 2006; Nagai et al. 2007;
Stanek et al. 2010; Rasia et al. 2012; Saro et al. 2012; Angulo
et al. 2012) and the evolution of gas and stars in clusters (e.g.,
Kravtsov et al. 2005; Ettori et al. 2006; Puchwein et al. 2010;
Young et al. 2011; Battaglia et al. 2013; Planelles et al. 2013).
Recent results have shown that it is necessary to include the
The Gould’s Belt Very Large Array Survey II:
The Serpens region
Gisela N. Ortiz-León1 , Laurent Loinard1,2 , Amy J. Mioduszewski3 , Sergio A. Dzib2 , Luis F.
Rodr´ıguez1,4 , Gerardo Pech1 , Juana L. Rivera1 , Rosa M. Torres5 , Andrew F. Boden6 , Lee
Hartmann7 , Neal J. Evans II8 , Cesar Brice˜
no9,10 , John Tobin11,12 , Marina A. Kounkel7 , and
Rosa A. González-Lópezlira1
g.ortiz@crya.unam.mx
–3–
ABSTRACT
We present deep (∼ 17 µJy) radio continuum observations of the Serpens
molecular cloud, the Serpens south cluster, and the W40 region obtained using
the Very Large Array in its A configuration. We detect a total of 146 sources,
29 of which are young stellar objects (YSOs), 2 are BV stars and 5 more are
associated with phenomena related to YSOs. Based on their radio variability
and spectral index, we propose that about 16 of the remaining 110 unclassified
sources are also YSOs. For approximately 65% of the known YSOs detected here
as radio sources, the emission is most likely non-thermal, and related to stellar
coronal activity. As also recently observed in Ophiuchus, our sample of YSOs
with X-ray counterparts lies below the fiducial G¨
udel & Benz relation. Finally,
we analyze the proper motions of 9 sources in the W40 region. This allows us to
better constrain the membership of the radio sources in the region.
Subject headings: astrometry - magnetic fields - radiation mechanisms: non-thermal radio continuum: stars - techniques: interferometric
Submitted to ApJ 2015-01-21, under review
THE DISTANCE TO NOVA V959 MON FROM VLA IMAGING
1
J. D. Linford , V. A. R. M. Ribeiro2,3 , L. Chomiuk1 , T. Nelson4 , J. L. Sokoloski5 , M. P. Rupen6 , K. Mukai7,8 ,
T. J. O’Brien9 , A. J. Mioduszewski10 , and J. Weston5
Submitted to ApJ 2015-01-21, under review
ABSTRACT
Determining reliable distances to classical novae is a challenging but crucial step in deriving their
ejected masses and explosion energetics. Here we combine radio expansion measurements from the
Karl G. Jansky Very Large Array with velocities derived from optical spectra to estimate an expansion
parallax for nova V959 Mon, the first nova discovered through its γ-ray emission. We spatially resolve
the nova at frequencies of 4.5–36.5 GHz in nine different imaging epochs. The first five epochs cover
the expansion of the ejecta from 2012 October to 2013 January, while the final four epochs span 2014
February to 2014 May. These observations correspond to days 126 through 199 and days 615 through
703 after the first detection of the nova. The images clearly show a non-spherical ejecta geometry.
Utilizing ejecta velocities derived from 3D modelling of optical spectroscopy, the radio expansion
implies a distance between 0.9 ± 0.2 and 2.2 ± 0.4 kpc, with a most probable distance of 1.4 ± 0.4 kpc.
This distance implies a γ-ray luminosity much less than the prototype γ-ray-detected nova, V407 Cyg,
possibly due to the lack of a red giant companion in the V959 Mon system. V959 Mon also has a
much lower γ-ray luminosity than other classical novae detected in γ-rays to date, indicating a range
of at least a factor of 10 in the γ-ray luminosities for these explosions.
Subject headings: white dwarfs — novae, cataclysmic variables — stars: individual (V959 Mon) —
gamma-rays — radio continuum
1. INTRODUCTION
The discovery of a γ-ray transient coincident with the
2010 nova event in V407 Cyg was a source of much
excitement and surprise for the nova and γ-ray communities alike (Abdo et al. 2010). Although MeV γrays produced by nuclear decay in nova ejecta have
been predicted for many years (e.g., Hernanz 2013,
and references therein), GeV emission from novae, as
detected with Fermi Large Area Telescope (LAT; Atwood et al. 2009), had received little attention prior to
the event in V407 Cyg (with the notable exception of
Tatischeff & Hernanz 2007). Abdo et al. (2010) suggested that a blast wave driven into the wind from the
Mira giant companion accelerated particles to relativistic speeds and produced γ-rays through either leptonic
or hadronic secondary interaction. In follow-up work exploring the X-ray properties of V407 Cyg, Nelson et al.
jlinford@.msu.edu
1 Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
2 Department of Astrophysics/IMAPP, Radboud University,
PO Box 9010, 6500 GL, Nijmegen, The Netherlands
3 Astrophysics, Cosmology, and Gravity Centre, Department
of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
4 School of Physics and Astronomy, University of Minnesota,
116 Church St SE, Minneapolis, MN 55455
5 Columbia Astrophysics Laboratory, Columbia University,
New York, NY, USA
6 Herzberg Institute of Astrophysics, National Research Council of Canada, Penticton, BC, Canada
7 Center for Space Science and Technology, University of
Maryland Baltimore County, Baltimore, MD 21250, USA
8 CRESST and X-ray Astrophysics Laboratory, NASA/GSFC,
Greenbelt MD 20771 USA
9 Jodrell Bank Centre for Astrophysics, Alan Turing Building,
University of Manchester, Manchester, M13 9PL, UK
10 National Radio Astronomy Observatory, P.O. Box 0, Socorro, NM 87801, USA
(2012) also claimed that the presence of a red giant companion was the primary characteristic of the system responsible for generating such a γ-ray event and efficient
acceleration of particles. They predicted that γ-ray emission from novae would be very rare, as most systems have
main sequence (MS) donors (see also L¨
u et al. 2011).
It did not take long for nature to prove this prediction incorrect. In 2012, the Fermi-LAT detected two
new transients that were spatially coincident with novae. The association of Fermi J1750-3243 with the nova
V1324 Sco was made within a few weeks of the outburst
(Cheung et al. 2012a). However, the nature of γ-ray
transient FGL J0639+0548 remained a mystery for several months after discovery (Cheung et al. 2012b), because its proximity to the sun prevented follow-up by
optical observers. When the region became optically
observable a few months after γ-ray detection, a nova
was discovered at the location of the Fermi transient
(Cheung et al. 2012c). Thus V959 Mon was the first
nova discovered in the γ-rays. In 2013, the two nakedeye visible novae V339 Del and V1369 Cen joined the
collection of novae detected in γ-rays (Hays et al. 2013,
Cheung et al. 2013, Ackermann et al. 2014).
The novae V1324 Sco, V959 Mon, V339 Del, and
V1369 Cen do not show evidence of an evolved
companion (Greimel et al. 2012; Wagner et al. 2012;
Darnley et al. 2013; Schaefer et al. 2014), making
them very different from V407 Cyg. Greimel et al. discuss the identification of the likely progenitor of V959
Mon in images obtained as part of the IPHAS survey (Drew et al. 2005). They find only a faint source
(r ≈ 17.9 mag) at the location of the nova, which is too
faint to be associated with a giant star within the Milky
Way. Furthermore, no spectral signatures of an evolved
Submitted to Astrophysical Journal
THE MASS AND RADII OF STRONGLY MAGNETIZED NEUTRON STARS
Farbod Kamiab, Avery E. Broderick, and Niayesh Afshordi
Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, ON N2L 2Y5, Canada
Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada
Submitted to Astrophysical Journal
ABSTRACT
It has been clear for some time now that super-critical surface magnetic fields, exceeding 4 × 1013
G, exist on a subset of neutron stars. These magnetars may harbor interior fields many orders of
magnitude larger, potentially reaching equipartition values. However, the impact of these strong
fields on stellar structure has been largely ignored, potentially complicating attempts to infer the
high density nuclear equation of state. Here we assess the effect of these strong magnetic fields on
the mass-radius relationship of neutron stars. We employ an effective field theory model for the
nuclear equation of state that includes the impact of hyperons, anomalous magnetic moments, and
the physics of the crust. We consider two magnetic field geometries, bounding the likely magnitude
of the impact of magnetic fields: a statistically isotropic, tangled field and a force-free configuration.
In both cases even equipartition fields have at most a 30% impact on the maximum mass. However,
the direction of the effect of the magnetic field depends on the geometry employed – force-free fields
leading to reductions in the maximum neutron star mass and radius while tangled fields increase both
– challenging the common intuition in the literature on the impact of magnetic fields.
Keywords: Neutron Stars, Pulsars, Magnetic Field, Magnetar
1. INTRODUCTION
Observations and theoretical studies of soft gammaray repeaters and X-ray pulsars point to the existence
of neutron stars with very high surface magnetic fields
(B > 1014 G), comprising the so-called magnetars (Duncan and Thompson 1992; Paczynski 1992; Thompson and
Duncan 1995, 1996; Melatos 1999). These surface magnetic fields are inferred through the observed slowing of
the stellar rotation, presumed to be a result of the emission of energy and angular momentum via large-scale
magnetic fields at the light cylinder, the point beyond
which they are unable to continue to rigidly rotate with
the star. This is expected to spin the star down on a
timescale ≈ P/P˙ ∝ B −2 P 4 , where P is the spin period.
Thus, magnetars are universally observed to have long
periods, roughly 1 s, and thus correspondingly large light
cylinders cP/(2π) ≈ 5 × 104 km. As a result, the implied
surface fields necessarily rely on a significant extrapolation, and typically assume a dipolar magnetospheric
magnetic field geometry, necessarily producing a lower
limit on the surface field strength, which is itself likely
to be a lower limit on the interior field strengths.
As a recent example, Gotthelf et al. (2013) monitored
the temporal and spectral evolution of a pulsar, originally
discovered by the NuSTAR X-ray Observatory, and from
the spin-down measurement, inferred a dipole magnetic
field strength B = 3 × 1014 G. Magnetars can also be
observed in the radio band. Follow-up observations of
the pulsar PSR J1622-4950, discovered by Levin et al.
(2010) in a survey of radio pulsars with the Parkes 64
m telescope, show that the pulsar has the highest inferred surface magnetic field of the known radio pulsars
(B ∼ 3×1014 G), making it the first magnetar discovered
via its radio emission. A catalog of 26 currently known
magnetars was presented recently by Olausen and Kaspi
fkamiab@pitp.ca
(2014).
The existence of extremely strong magnetic fields observed in magnetars can be explained by a number of processes. Neutron stars with strong magnetic dipole fields
B ∼ 1014 - 1015 G, can form when conditions for efficient
helical dynamo action are met during the first few seconds after gravitational collapse (Duncan and Thompson
1992). In addition to differential rotation, convection
may play a significant role in amplifying the magnetic
field (Thompson and Duncan 1993). In the context of
more sophisticated simulations of field amplification in
non-rotating stellar cores during the collapse and postbounce accretion phases of a supernova, including magnetohydrodynamics and neutrino transport, it was found
that initial magnetic field strengths stronger than 1010
G could yield magnetar-like final field strengths (Obergaulinger et al. 2014).
As neutron stars with very strong magnetic fields appear to exist in nature, one is tempted to ask how these
field strengths affect the structure of these stars. This
is particularly important as the equilibrium mass and
radius of neutron stars vary based on the nuclear and
gravitational physics assumed (for example, see Lattimer
and Prakash (2001, 2007) for the effects of various nuclear equations of state on the structure of neutron stars,
and see Kamiab and Afshordi (2011); Pani et al. (2011);
Alavirad and Weller (2013) for effects of modifying general relativity). As a result, observational measurements
of these masses and radii have the potential to constrain theoretical models. In particular, observing neutron stars with very high masses is useful, as each set
of models (nuclear equation of state and gravitational
model) predicts a maximum mass beyond which no neutron stars would exist. For example, the detection of a
1.97 ± 0.04 M pulsar by Demorest et al. (2010), or the
measurement of a 2.01 ± 0.04 M pulsar by Antoniadis
et al. (2013) have been used to significantly constrain
STELLAR SUBSTRUCTURES AROUND THE HERCULES DWARF SPHEROIDAL GALAXY
T. A. Roderick 1 , H. Jerjen1 , A. D. Mackey1 , and G. S. Da Costa1
Research School of Astronomy and Astrophysics, Australian National University,
Canberra, ACT 2611, Australia
ABSTRACT
We present deep g, i-band DECam stellar photometry of the Hercules Milky Way satellite galaxy,
and its surrounding field, out to a radial distance of 5.4 times the tidal radius. We have identified nine
extended stellar substructures associated with the dwarf; preferentially distributed along the major
axis of the galaxy. Two significant over-densities lie outside the 95% confidence band for the likely
orbital path of the galaxy and appear to be free-floating tidal debris. We estimate the luminosity of
the new stellar substructures, and find that approximately the same amount of stellar flux is lying in
these extended structures as inside the main body of Hercules. We also analyse the distribution of
candidate blue-horizontal-branch stars and find agreement with the alignment of the substructures at
a confidence level greater than 98%. Our analysis provides a quantitative demonstration that Hercules
is a strongly tidally disrupted system, with noticeable stellar features at least 1.9 kpc away from the
galaxy.
Subject headings: galaxies: dwarf (galaxies:) Local Group
1. INTRODUCTION
Ultra-faint Milky Way (MW) satellite galaxies are the
most dark matter dominated stellar systems in the Universe (Mateo 1998; Simon & Geha 2007; McConnachie
2012). The high mass-to-light ratios seen in these
pressure-dominated systems are determined from their
velocity dispersion, which assumes that the underlying
stellar populations are in dynamic-equilibrium. However, satellite galaxies interacting with their hosts can
undergo significant tidal stirring (Lokas et al. 2012), leaving kinematic samples potentially contaminated by unbound stars (Klimentowski et al. 2007). In the case where
a galaxy is being tidally disrupted, the mass-to-light ratio can be overestimated, and this may not be apparent
in the galaxy’s dispersion profile (Pe˜
narrubia et al. 2008).
It is also possible for a galaxy that has undergone tidal
disruption to retain its spherical shape (Mu˜
noz et al.
2008).
The dynamical state of a satellite galaxy is thus a
highly relevant question. For that reason it is important to search for signs of tidal disruption not only in
the central region of these galaxies, but in the vicinity
around them where tidal debris may be present. The
MW satellites provide an excellent opportunity for this
type of investigation, as they are close enough to be resolved into individual stars and can be studied in great
detail (see Tolstoy et al. 2009; McConnachie 2012; Jerjen
2012, for a discussion and census of local satellites).
Comprehensive studies of the MW satellite galaxies
have led to numerous investigations of their role in
galaxy formation. In the ΛCDM cosmological paradigm,
galaxies form hierarchically through merger and accretion of smaller structures (Blumenthal et al. 1984; Van
Den Bosch et al. 2005; Giocoli et al. 2009). Moore et al.
(1999) demonstrated that dark matter sub-structure occurs on galactic scales, resulting in galaxy halos appearing as scaled versions of galaxy clusters. Mergers and acTammy.Roderick@anu.edu.au
cretion are a feature of galaxy clusters, therefore the outskirts of larger galaxies should also show signs of merger
and accretion events (Diemand et al. 2007). A rather
striking example in this context is Andromeda (M31),
which possesses numerous satellite systems and copious
substructure in its stellar halo (McConnachie et al. 2009;
Ibata et al. 2014). Substructures are also observed in our
own Milky Way in the form of stellar streams (e.g. Newberg 2002; Belokurov et al. 2007a; Grillmair 2006; Newberg et al. 2010; Sesar et al. 2013; Grillmair 2014), with
perhaps the quintessential example being the Sagittarius
dwarf (Ibata et al. 1994), and its great tidal tails strewn
across the sky (Majewski et al. 2003; Newby et al. 2013).
Contrary to the predictions of ΛCDM, Kroupa et al.
(2005) demonstrated that the distribution of the MW
satellite population is inconsistent with that of a
dwarf galaxy population drawn from cosmological substructure. Further investigation of the satellite populations of both the MW and M31 has found, in both cases,
that the satellites have a disc-like distribution with high
inclination to the plane of the host galaxy (Metz et al.
2005, 2007, 2009; Pawlowski et al. 2013; Ibata et al. 2013;
Conn et al. 2013). This has led to the alternative picture
that a significant fraction of the currently known MW
satellite galaxies is of tidal origin (Kroupa et al. 2010;
Pawlowski et al. 2014); forming from a major collision of
the MW and another galaxy. This theory accounts for
many of the observed features of the dwarf galaxy population, including the high mass-to-light ratios (explained
as systems driven out of equilibrium (Yang et al. 2014)).
Learning whether or not the dwarf population is largely
comprised of systems driven out of equilibrium, or shows
signs more indicative of hierarchical build-up, may be a
key factor in determining the origin of the population as
a whole. Most of the research into the MW dwarf galaxy
population to date has been restricted to the main stellar
body of each dwarf. However, it is in the outer regions
where we expect to see more subtle signs of tidal disruption. The obvious example is Sagittarius (Ibata et al.
The current impact flux on Mars and its seasonal variation
Youngmin JeongAhn and Renu Malhotra
Lunar and Planetary Laboratory, The University of Arizona, Tucson, AZ 85721, USA.
jeongahn@lpl.arizona.edu,renu@lpl.arizona.edu
ABSTRACT
We calculate the present-day impact flux on Mars and its variation over the
Martian year, using the current data on the orbital distribution of known Mars¨
crossing minor planets. We adapt the Opik-Wetherill
formulation for calculating
collision probabilities, paying careful attention to the non-uniform distribution of
the perihelion longitude and the argument of perihelion owed to secular planetary
perturbations. We find that these previously neglected non-uniformities have a
significant effect on the mean annual impact flux as well as its seasonal variation.
The impact flux peaks when Mars is at aphelion, but the near-alignment of Mars’
eccentricity vector with the mean direction of the eccentricity vectors of Marscrossers causes the mean annual impact flux as well as the amplitude of the
seasonal variation to be significantly lower than the estimate based on a uniform
random distribution of perihelion longitudes of Mars-crossers. We estimate that
the flux of large impactors (of absolute magnitude H < 16) within ±30◦ of Mars’
aphelion is about four times larger than when the planet is near perihelion.
Extrapolation of our results to a model population of meter-size Mars-crossers
shows that if these small impactors have a uniform distribution of their angular
elements, then their aphelion-to-perihelion impact flux ratio would be as large
as 25. These theoretical predictions can be tested with observational data of
contemporary impacts that is becoming available from spacecraft currently in
orbit about Mars.
1.
Introduction
The impact crater record on the surfaces of the terrestrial planets over geologically
long timescales provides a window on the dynamical history of the solar system, including
a chronology of major geological and dynamical events. This crater-based chronology is
calibrated primarily on estimates of the cratering rate on the Moon over geological timescales.
The presence of space observatories in orbit about Mars now offers a new opportunity to
Planet formation around binary stars: Tatooine made easy
Benjamin C. Bromley
Department of Physics & Astronomy, University of Utah,
115 S 1400 E, Rm 201, Salt Lake City, UT 84112
bromley@physics.utah.edu
Scott J. Kenyon
Smithsonian Astrophysical Observatory,
60 Garden St., Cambridge, MA 02138
skenyon@cfa.harvard.edu
ABSTRACT
We examine characteristics of circumbinary orbits in the context of current
planet formation scenarios. Analytical perturbation theory predicts the existence
of nested circumbinary orbits that are generalizations of circular orbits in a Keplerian potential. They contain forced epicyclic motion aligned with the binary as
well as higher frequency oscillations, yet they do not cross, even in the presence of
massive disks and perturbations from large planets. For this reason, dissipative
gas and planetesimals can settle onto these “most circular” orbits, facilitating the
growth of protoplanets. Outside a region close to the binary where orbits are generally unstable, circumbinary planets form in much the same way as their cousins
around a single star. Here, we review the theory and confirm its predictions with
a suite of representative simulations. We then consider the circumbinary planets
discovered with NASA’s Kepler satellite. These Neptune- and Jupiter-size planets, or their planetesimal precursors, may have migrated inward to reach their
observed orbits, since their current positions are outside of unstable zones caused
by overlapping resonances. In situ formation without migration seems less likely,
only because the surface density of the protoplanetary disks must be implausibly
high. Otherwise, the circumbinary environment is friendly to planet formation,
and we expect that many Earth-like “Tatooines” will join the growing census of
circumbinary planets.
Subject headings: planetary systems – planets and satellites: formation – planets and satellites: dynamical evolution and stability – planets and satellites:
individual (Kepler-16b, Kepler-34b, Kepler-35b, Kepler-38a, Kepler-47b, PH1,
Kepler-413b) – planet disk interactions – stars: binaries
EXTRACTING RADIAL VELOCITIES OF A- AND B-TYPE STARS
FROM ECHELLE SPECTROGRAPH CALIBRATION SPECTRA
Juliette C. Becker1,2,3 , John Asher Johnson4,5 , Andrew Vanderburg3,4 , Timothy D. Morton6
ABSTRACT
We present a technique to extract radial velocity measurements from echelle spectrograph observations of rapidly rotating stars (V sin i & 50 km s−1 ). This type of measurement is difficult because
the line widths of such stars are often comparable to the width of a single echelle order. To compensate for the scarcity of lines and Doppler information content, we have developed a process that
forward–models the observations, fitting the radial velocity shift of the star for all echelle orders
simultaneously with the echelle blaze function. We use our technique to extract radial velocity measurements from a sample of rapidly rotating A– and B–type stars used as calibrator stars observed
by the California Planet Survey observations. We measure absolute radial velocities with a precision
ranging from 0.5–2.0 km s−1 per epoch for more than 100 A- and B-type stars. In our sample of
10 well-sampled stars with radial velocity scatter in excess of their measurement uncertainties, three
of these are single–lined binaries with long observational baselines. From this subsample, we present
detections of two previously unknown spectroscopic binaries and one known astrometric system. Our
technique will be useful in measuring or placing upper limits on the masses of sub-stellar companions
discovered by wide–field transit surveys, and conducting future spectroscopic binarity surveys and
Galactic space–motion studies of massive and/or young, rapidly–rotating stars.
Subject headings: binaries: general — methods: data analysis — techniques: radial velocities
1. INTRODUCTION
Stellar radial velocity (RV) measurements have become
increasingly precise over the past 30 years due to the advent and development of high–resolution spectrographs
equipped with digital detectors (Campbell et al. 1981),
including HIRES at Keck (Vogt et al. 1994; Howard
et al. 2010); and particularly with the construction
of environmentally-stabilized spectrometers such as the
HARPS-South and -North spectrographs (Mayor et al.
2003; Cosentino et al. 2012), SOPHIE at Haute-Provence
(Bouchy et al. 2009), CHIRON at CTIO (Schwab et
al. 2010), and the Planet Finder Spectrograph (PFS)
at Magellan (Crane et al. 2006, 2010). While the discovery and characterization of exoplanets has been the
driving scientific motivation behind these developments
(e.g. Mayor & Queloz 1995; Butler et al. 1999, 2004; Dumusque et al. 2012), increased measurement precision has
also led to significant advances in understanding stellar
binarity, particularly around Sun-like stars (Duquennoy
& Mayor 1991; Fischer & Marcy 1992; Raghavan et al.
2010).
However, the stability of a given spectrometer is only
part of what enables high radial velocity precision. The
attainable Doppler precision also depends greatly on the
type of star observed. Measurements at the highest atjcbecker@umich.edu
1 Department of Astronomy, University of Michigan, 1085 S
University Ave, Ann Arbor, MI 48109
2 Cahill Center for Astronomy and Astrophysics, California
Institute of Technology, 1200 E. California Blvd., Pasadena, CA
91125
3 NSF Graduate Research Fellow
4 Harvard-Smithsonian Center for Astrophysics, 60 Garden
St., Cambridge, MA 02138
5 David & Lucile Packard Fellow
6 Department of Astrophysical Sciences, 4 Ivy Lane, Peyton
Hall, Princeton University, Princeton, NJ 08544
tainable precision today, levels at or below 1 m s−1 , can
only be performed on stars with spectra that contain
many sharp spectral lines. As a result, most RV–based
planet surveys have been restricted to F-,G-,K-,and Mtype dwarf stars, which rotate slowly and display numerous fine spectral features.
On the other hand, more massive A- and B-type stars
have hotter atmospheres and exhibit fewer absorption
features. Also, because these hot stars lack convective
outer layers, they retain most of their primordial angular momentum, and what few spectral features they
show are highly rotationally broadened. For these reasons, rapidly–rotating hot and massive stars have nearly
featureless blackbody spectra, showing only very broad
hydrogen and helium absorption lines, as illustrated in
Figure 1. Rotational smearing also affects young stars
of all masses if they have not yet lived long enough to
have experienced sufficient magnetic braking. It is thus
much more challenging to obtain precise RVs for rapidly
rotating stars from high–resolution echelle observations.
At the same time, their nearly featureless spectra make
hot stars excellent calibrators for measuring and removing telluric absorption features, and as calibrators for
Doppler surveys (as well as for instrumental tests, as in
Spronck et al. 2013). These “blackbodies in the sky”
are excellent calibrators of the transmission functions
of absorption cells used as wavelength references, and
as means of measuring the spectrometer’s instrumental
profile for surveys using gas absorption cells. As a result, there exists a large library of high–resolution spectra of hot stars obtained as calibrators of high-precision,
gas-cell calibrated Doppler surveys such as the California
Planet Survey (CPS).
While this library was obtained for calibration purposes rather than as a scientific data product, it serendip-
D RAFT VERSION M ARCH 16, 2015
THE EVENT HORIZON OF M87
AVERY E. B RODERICK 1,2 , R AMESH NARAYAN 3 , J OHN KORMENDY 4,5,6 ,
E RIC S. P ERLMAN 7 , M ARCIA J. R IEKE 8 , AND S HEPERD S. D OELEMAN 3,9
1 Perimeter Institute for Theoretical Physics, 31 Caroline Street North, Waterloo, ON, N2L 2Y5, Canada
Department of Physics and Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, ON, N2L 3G1, Canada
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, 02138
4 Department of Astronomy, University of Texas at Austin, 2515 Speedway, Mail Stop C1400, Austin, TX 78712-1205, USA; kormendy@astro.as.utexas.edu
5 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching-bei-München, Germany
6 Universitäts-Sternwarte, Scheinerstrasse 1, D-81679 München, Germany
7 Department of Physics and Space Sciences, 150 W. University Blvd., Florida Institute of Technology, Melbourne, FL 32901, USA; eperlman@fit.edu
8 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721-0065
9 MIT Haystack Observatory, Off Route 40, Westford, MA 01886, USA
2
ABSTRACT
The 6 × 109 M⊙ supermassive black hole at the center of the giant elliptical galaxy M87 powers a relativistic
jet. Observations at millimeter wavelengths with the Event Horizon Telescope have localized the emission from
the base of this jet to angular scales comparable to the putative black hole horizon. The jet might be powered
directly by an accretion disk or by electromagnetic extraction of the rotational energy of the black hole. However,
even the latter mechanism requires a confining thick accretion disk to maintain the required magnetic flux near the
black hole. Therefore, regardless of the jet mechanism, the observed jet power in M87 implies a certain minimum
mass accretion rate. If the central compact object in M87 were not a black hole but had a surface, this accretion
would result in considerable thermal near-infrared and optical emission from the surface. Current flux limits on
the nucleus of M87 strongly constrain any such surface emission. This rules out the presence of a surface and
thereby provides indirect evidence for an event horizon.
Subject headings: black hole physics – galaxies: individual (M87) – gravitation – radio continuum: galaxies –
infrared: galaxies – ultraviolet: galaxies
1. INTRODUCTION
It is now widely accepted that active galactic nuclei (AGN)
are powered by supermassive objects (reaching 1010 M⊙ ) that
are sufficiently compact to exclude all other astrophysically
credible alternatives to black holes (Rees 1984). However, it is
less clear that these objects possess the defining characteristic
of a black hole: an event horizon1. The existence of black
hole event horizons plays a central role in a number of
puzzles associated with black holes, e.g., the information
paradox. A number of recent results suggest that a resolution
of these puzzles may result in modifications on horizon scales
(e.g., Mathur 2011; Almheiri et al. 2013; Mathur 2014), which
provides strong motivation for seeking astronomical evidence
for the reality of event horizons.
Accretion onto compact objects with a surface, e.g., white
dwarfs, neutrons stars, results in the formation of a boundary
layer in which any remaining kinetic energy contained within
the accretion flow is thermalized and radiated. In contrast, gas
accreting onto a black hole is free to advect any excess energy
across the horizon without further observational consequence.
˙ can be independently estimated,
If the mass accretion rate, M,
this difference provides an observational means to distinguish
between the presence of a surface, or more accurately a
“photosphere,” and a horizon.
The above argument has already been used to argue
1 Here we will employ an astrophysically motivated definition of the
horizon: a surface from inside which astronomical signals cannot propagate
to large distances in astronomically relevant timescales. Formally, for a
dynamical system, such a surface is identified with the apparent horizon.
However, in the context of astrophysical black holes described by general
relativity, it corresponds to the event horizon as well.
for the existence of event horizons in X-ray binaries by
comparing neutron star and black hole systems in aggregate (Narayan et al. 1997; Garcia et al. 2001; Narayan & Heyl
2002; Done & Gierliński 2003; Narayan & McClintock 2008).
However, the advent of horizon-resolving observations, enabled by millimeter-wavelength very long baseline intererometric observations (mm-VLBI) carried out by the Event Horizon Telescope (EHT, Doeleman et al. 2009; Doeleman 2010;
Doeleman et al. 2008; Fish et al. 2011; Doeleman et al. 2012),
has made it possible to extended the argument to individual
systems. This is primarily because restricting the size of any
photospheric emission to horizon scales enables two important
simplifications:
1. Any putative photosphere that lies within the photon
orbit is expected to radiate to a good approximation
like a blackbody, independently of the details of its
composition (Broderick & Narayan 2006, 2007). This
is because a majority of the photons emitted from
the photosphere will be strongly lensed back onto the
photosphere, thermally coupling the photosphere to
itself and to the emitted photon field. As the redshift
of the surface increases, the blackbody approximation
becomes increasingly accurate.
2. The expected temperature of the photosphere emission,
as seen by distant observers, is dependent upon the
˙ and the apparent photosphere size,
mass accretion rate M
the latter of which is fixed when the photosphere lies
within the photon orbit. Thus, assuming that the system
has reached steady state2 , any independent estimate of
2
The additional gravitational time delay for radiation to escape from
version March 16, 2015: fm
OPTICAL SPECTROSCOPIC OBSERVATIONS OF BLAZARS AND γ-RAY BLAZAR CANDIDATES
IN THE SLOAN DIGITAL SKY SURVEY DATA RELEASE NINE
F. Massaro1 , N. Masetti3 , R. D’Abrusco4 , A. Paggi4 , & S. Funk2
version March 16, 2015: fm
ABSTRACT
We present an analysis of the optical spectra available in the Sloan Digital Sky survey data release
nine (SDSS DR9) for the blazars listed in the ROMA-BZCAT and for the γ-ray blazar candidates
selected according to their IR colors. First, we adopt a statistical approach based on MonteCarlo
simulations to find the optical counterparts of the blazarslisted in the ROMA-BZCAT catalog. Then
we crossmatched the SDSS spectroscopic catalog with our selected samples of blazars and γ-ray blazar
candidates searching for those with optical spectra available to classify our blazar-like sources and,
whenever possible, to confirm their redshifts. Our main objectives are determining the classification
of uncertain blazars listed in the ROMA-BZCAT and discovering new gamma-ray blazars. For the
ROMA-BZCAT sources we investigated a sample of 84 blazars confirming the classification for 20 of
them and obtaining 18 new redshift estimates. For the γ-ray blazars, indicated as potential counterparts of unassociated Fermi sources or with uncertain nature, we established the blazar-like nature of
8 out the 27 sources analyzed and confirmed 14 classifications.
Subject headings: methods: statistical - galaxies: active - quasars: general - surveys - radiation mechanisms: non-thermal
1. INTRODUCTION
According to the well assessed unification scenario of the active galactic nuclei (AGN; e.g.,
Antonucci 1993; Urry & Padovani 1995) blazars are radio loud sources, featuring compact radio cores combined with a “flat” radio spectra that extends from
frequencies below ∼1GHz (e.g., Massaro et al. 2013a;
Massaro et al. 2013b; Nori et al. 2013) up to the submillimeter band (e.g., Giommi et al. 2012). They are
characterized by a variable, non-thermal, continuum
and exhibit a typical double bumped spectral energy
distribution (SED), and represent the largest known
population of γ-ray sources (e.g., Abdo et al. 2010a;
Ackermann et al. 2011) proving the most relevant contribution to the extragalactic γ-ray background (e.g.,
Mukherjee et al. 1997; Abdo et al. 2010b).
Blazars are generally classified on the basis of their
optical spectra and divided in two main classes: i) BL
Lac objects, labeled as BZBs according to the nomenclature of the ROMA-BZCAT5 (Massaro et al. 2009;
Massaro et al. 2011a) when presenting featureless optical spectra and ii) flat spectrum radio quasars (hereinafter BZQs) having a typical quasar-like optical appearance but also featuring high and variable optical polarization. In particular, blazars are classified as BZB if
the rest-frame equivalent width of their optical features
is lower than 5 ˚
A (Stickel et al. 1991; Stoke et al. 1991;
1 Yale Center for Astronomy and Astrophysics, Physics Department, Yale University, PO Box 208120, New Haven, CT
06520-8120, USA
2 SLAC National Laboratory and Kavli Institute for Particle
Astrophysics and Cosmology, 2575 Sand Hill Road, Menlo Park,
CA 94025, USA
3 INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica di
Bologna, via Gobetti 101, 40129, Bologna, Italy
4 Harvard - Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA 02138, USA
5 http://www.asdc.asi.it/bzcat/
Laurent-Muehleisen et al. 1999; Landoni et al. 2013).
As recently discovered using the WISE all-sky survey (Wright et al. 2010), blazars show by peculiar infrared (IR) colors (Massaro et al. 2011b) mostly due
to their non-thermal continuum that allowed to distinguish them from other classes of active galaxies (e.g.,
D’Abrusco et al. 2012; Massaro et al. 2012a). This IR
property was also interpreted as due to the lack of observational signatures form a dusty torus in the case of
BZBs (e.g., Plotkin et al. 2012).
The variable, non-thermal emission of both BZBs
and BZQs, extending from radio up to TeV energies,
is interpreted as arising from high-energy particles accelerated in a relativistic jet oriented along to the
line of sight, whereas relativistic effects amplifies both
their luminosity and the amplitude of their variability
(Blandford & Rees 1978; Giommi et al. 2013).
Recently,
we searched for blazar-like objects as potential counterparts of the unidentified γ-ray sources (UGSs) observed with Fermi
(Abdo et al. 2010a;
Nolan et al. 2012) with several methods based on the IR colors alone
(Massaro et al. 2012b;
D’Abrusco et al. 2013)
or
combined with other multifrequency observations,
as radio (Massaro et al. 2013d) or X-ray properties
(Paggi et al. 2013). We also explored the use of low
radio frequency observations (i.e., below ∼1 GHz)
as an alternative possibility to find blazar-like counterparts (e.g., Massaro et al. 2013a; Nori et al. 2013)
for the UGSs listed in the second Fermi-Large Area
Telescope (LAT) catalog (2FGL, Nolan et al. 2012)
in addition to other multifrequency analysis (e.g.,
Mirabal & Halpern 2009;
Ackermann et al. 2012;
Cowperthwaite et al. 2013; Masetti et al. 2013).
All
these investigations provided several lists of gamma-ray
blazar candidates that has to be confirmed and classified
via optical spectroscopy.
Here we investigate the optical spectra of two
QED Plasma and Magnetars
Marat Freytsis and Samuel E. Gralla
Center for the Fundamental Laws of Nature, Harvard University, Cambridge, MA 02138, USA
Magnetars are surrounded by diffuse plasma in magnetic field strengths well above the quantum electrodynamic critical value. We derive equations of “quantum force-free electrodynamics” for this plasma using an
effective field theory arguments. We argue that quantum effects do not modify the large scale structure of the
magnetosphere, and in particular that the spin-down rate does not deviate significantly from the classical result.
We provide definite evolution equations that can be used to explore potentially important small-scale corrections, such as shock formation, which has been proposed as a mechanism for both burst and quiescent emission
from magnetars.
Introduction — From the earliest days of the quantum
theory of light, before even the development of quantum
electrodynamics (QED) proper, it was recognized that quantum effects should become important in electromagnetic field
strengths of order m2 /(e¯h), where m and e are the mass and
charge of the electron [1, 2]. Near this “Schwinger limit,”
new effective photon-photon interactions emerge, mediated
by electron loops, leading to phenomena such as vacuum birefringence and light-by-light scattering. Most dramatically,
strong electric fields create electron-positron pairs out of the
vacuum, a non-perturbative effect [3]. The most promising
route to reaching these field strengths in the laboratory is the
use of high-intensity lasers [4]. While some of the effects may
be observable in upcoming facilities, the actual field strengths
will still be well below the Schwinger limit.
Fortunately, nature provides us with another avenue to
investigate strong-field QED: a class of astrophysical objects known as magnetars. Magnetars are pulsars (rotating,
magnetized neutron stars) with exceptionally strong surface
magnetic field strengths. In fact, magnetars can have field
strengths of up to 1015 G and maybe higher, which exceed the
critical field strength,
BQ =
m2
≈ 4.4 × 1013 G,
h¯ e
(1)
by two orders of magnitude! Much work has been devoted to
understanding the physical processes that take place in such
magnetic field strengths; see [5–7] for reviews.
Most of this work is done assuming a vacuum environment,
whereas in fact magnetars (and pulsars in general) are surrounded by a diffuse plasma. The existence and properties
of this plasma can be understood from the smallness of the
dimensionless parameter
χ=
m
≈ 10−15 .
eBR
(2)
Here B is the magnetic field strength, R is the stellar radius,
and we have assumed canonical pulsar values B ≈ 1012 G and
R ≈ 10 km.
This number accounts for the plasma as follows [8, 9]. A
conductor moving with velocity v in a magnetic field B generates an electric field of order Bv by “unipolar induction”.
For a rotating magnetized sphere in vacuum this electric field
has a component along B, and hence can accelerate particles.
The energy to which the particles can be accelerated over a
typical system size is thus eBvR. Computing v/ χ shows that
this energy exceeds the rest mass of the electron by many
orders of magnitude. (For pulsars a typical surface velocity
is v ∼ 10−4 .) Thus any stray charges are rapidly accelerated to above the pair-production threshold, and the ensuing
pair-creation cascade will populate the magnetosphere with
plasma.
As charges are generated they will arrange themselves to
cancel the electric field, driving the Lorentz invariant E · B to
zero. Production ceases as this invariant becomes too small to
produce the required acceleration. For charge corotating with
the star the density required to cancel E · B is the so-called
Goldreich–Julian charge density vB/R. This sets a typical
scale for the plasma mass density, mvB/(eR). The ratio of
the particle mass/energy density to the electromagnetic field
energy density is then vχ , which is exceedingly tiny, making
the plasma dynamics completely dominated by the field.
Assuming classical electrodynamics, such plasmas are described by a non-linear theory of the electromagnetic field
known as force-free electrodynamics (FFE) [8, 10–12]. The
theory follows from the assumption that the electromagnetic
stress-energy is conserved on its own, leading to the condition
that the Lorentz force density everywhere vanishes. Naively,
one might expect any classical description to break down at
or near the critical field strength BQ . The measurement of
the surface magnetic field strength of a pulsar/magnetar relies
on the dipole radiation spin-down formula, which has only
been derived in classical electrodynamics (vacuum or forcefree [13, 14]) or in vacuum QED [15]. Thus the very evidence
for super-critical magnetic fields in nature is sensitive to the
question of magnetically dominated QED plasma.
In this letter we will derive equations of “quantum forcefree electrodynamics” to describe this plasma. The strategy is
to integrate out electron loop fluctuations from the QED action, following the basic approach established by Euler and
Heisenberg (EH) in 1935 [2]. However, the EH calculation
is done assuming no fermion in- or out-states, allowing the
electron to be integrated out entirely in the effective action,
whereas we wish to consider plasma. We therefore proceed
in two steps. First, we consider a collisionless multiparticle
system and use effective field theory (EFT) arguments to establish the size and form of the modifications due to QED. We
then show that the modifications that survive in the magnetically dominated limit follow from the EH Lagrangian, without requiring a new QED calculation. We thereby write down
The incidence of magnetic fields in cool DZ white dwarfs
M.A. Hollands1, B.T. Gänsicke1, D. Koester2
1
2
Department of Physics, University of Warwick, Coventry CV4 7AL, UK
Institut f¨
ur Theoretische Physik und Astrophysik, University of Kiel, 24098 Kiel, Germany
Accepted 2015 March 12.
ABSTRACT
Little is known about the incidence of magnetic fields among the coolest white dwarfs.
Their spectra usually do not exhibit any absorption lines as the bound-bound opacities
of hydrogen and helium are vanishingly small. Probing these stars for the presence of
magnetic fields is therefore extremely challenging. However, external pollution of a
cool white dwarf by, e.g., planetary debris, leads to the appearance of metal lines
in its spectral energy distribution. These lines provide a unique tool to identify and
measure magnetism in the coolest and oldest white dwarfs in the Galaxy.
We report the identification of 7 strongly metal polluted, cool (Teff < 8000 K)
white dwarfs with magnetic field strengths ranging from 1.9 to 9.6 MG. An analysis of
our larger magnitude-limited sample of cool DZ yields a lower limit on the magnetic
incidence of 13 ± 4 percent, noticeably much higher than among hot DA white dwarfs.
Key words: stars: white dwarfs - stars: magnetic field - stars: planetary systems stars: evolution
1
INTRODUCTION
White dwarfs (WDs) have been known to harbour magnetic fields since the detection of circularly polarised light
from GJ 742 (Kemp et al. 1970). In the following decades
a plethora of magnetic WDs (MWDs) have been identified either from Zeeman splitting of absorption lines
in their spectra or by spectropolarimetry (Kawka et al.
2007, and references therein). A wide variety is seen in
temperature, atmospheric composition, and field strength.
The advent of large scale spectroscopic surveys, in particular the Sloan Digital Sky Survey (SDSS), has in
the last decade increased the number of known MWDs
to several hundred (G¨
ansicke et al. 2002; Schmidt et al.
2003; Vanlandingham et al. 2005; Kleinman et al. 2013;
Kepler et al. 2013, 2015).
Despite the ever growing list of these previously rare
objects, two questions continue to remain without a definite
answer: What is the origin of these magnetic fields? And
what is the fraction of WDs that are magnetic, and how
does this vary with cooling age/temperature?
Two distinct models have been proposed to explain
the emergence of fields & 1 MG in isolated WDs. In the
fossil field hypothesis, the magnetic fields of the chemically peculiar Ap/Bp stars are thought to be amplified
due to flux conservation during post-main sequence evolution resulting in WDs with fields in the MG regime
(Woltjer 1964; Angel & Landstreet 1970; Angel et al. 1981;
Wickramasinghe & Ferrario 2000). A more recent hypothc 2015 RAS
esis (Tout et al. 2008) considers a binary origin, where a
system undergoing a common envelope leads to magnetic
dynamo generation.
The incidence of magnetism in WDs remains poorly estimated due to selection effects. Independent studies are difficult to reconcile with one another as each suffers from its
own set of biases. This problem becomes significantly more
pronounced when focusing on subsets of the total WD population where small number statistics dominate. Recent volume limited samples of nearby WDs present the most unbiased estimates of the magnetic incidence when considering
all WD sub types, and suggest incidences of 21 ± 8 percent
for WDs within 13 pc of the Sun, and 13±4 percent for those
within 20 pc (Kawka et al. 2007). However these MWDs are
dominated by fields lower than 100 kG and strongly magnetic objects with fields above 10 MG. Only 1 out of the 15
MWDs in the compilation of Kawka et al. (2007) has a field
strength between 1 and 10 MG (the range that we discuss in
this work). More recently, Sion et al. (2014) have presented
a volume limited WD sample within 25 pc from the Sun.
They find a magnetic incidence of 8 percent when considering magnetic fields above 2 MG only. Other studies have
investigated the magnetic incidence with much larger, but
magnitude-limited samples. For instance Kleinman et al.
(2013) identified over 12000 DAs1 from SDSS data release 7
1
WDs showing only hydrogen/helium lines in their spectra are
classified DA/DB, with only metal lines as DZ, and without any
spectral lines as DC. Magnetic DA WDs where magnetism is de-

Magnetic susceptibility, magnetization, magnetic moment and

Transcription

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