Studi di rotazione stellare con i da% di PLATO

Studi di rotazione stellare con i da0 di PLATO Sergio Messina INAF-­‐Osservatorio Astrofisico di Catania
‘Contributo italiano alla missione PLATO’ Why studying rota0on? Rota%on plays a key role in: Rota%on allows us to: Magne0c ac0vity Map the features of ac0vity Planet forma0on Remove effect of ac0vity on other observables Close binary system evolu0on Li deple0on … Constrain the star’s age Inves0gate the internal structure (core-­‐envelope coupling) … Example of photometric time series
from space-born observation
Information from photometric data
time series
1.  Stellar rota0on period 2.  Surface differen0al rota0on 3.  Time-­‐scale of Ac0ve Region Growth and Decay 4.  Magne0c ac0vity level in the photosphere 5.  Maps of photospheric ac0ve regions 1. Stellar rota0on period The stellar rota0on modulates the visibility of ac0ve regions and, consequently, determines a quasi-­‐periodic modula0on of the observed stellar flux. The period of the flux modula0on is the stellar rota0on period. Different algorithms allow us to iden0fy periodici0es in data 0me series : •  Lomb-­‐Scargle periodogram •  CLEAN periodogram •  Phase dispersion minimiza0on •  Amplitude of Varia0on •  …. The use of all algorithms is advisable to assign a quality flag to the derived rota%on period. Example of Lomb-Scargle periodogram
2. Surface Differen0al Rota0on (SDR) It can be derived from •  Double peaks in the periodogram •  Rota0on period varia0ons •  Phase migra0on of light-­‐curve minimum SDR from double peaks Example of star with two ac%ve longitudes on opposite hemispheres Modula%on arising from primary spot P=4.33d Modula%on arising from secondary spot P=4.35d Spot 1 (primary spot)  Pd=4.3300+/-­‐0.0005 Spot 2 (secondary spot)  Pd=4.3500+/-­‐0.0005 (=2.175 x 2) SDR from period varia0on Messina & Guinan 2003, A&A 409, 1017 Case of an0-­‐solar pa^ern: rota0on period increases towards the spot cycle maximum Rodonò et al. 2000, A&A 358, 624 Case of solar pa^ern: rota0on period decreases towards the spot cycle maximum SDR from migra0on of phase of minimum Messina et al. in prepara%on 3. Time-­‐scale of Ac0ve Region Growth and Decay (ARGD) A) Star with dis%nct plateau ARGD can be determined from pooled variance analysis, that is the variance in photometric 0me series over different 0me scales Rota%on period B) AR evolu%on-­‐
dominated star Rota%on period ARGD determina0on allows us to assign a confidence level to SDR detec0on. In case A) the period determina0on is reliable; in case B) it can be affected by the ARGD 4. Level of photospheric ac0vity F-­‐type star K-­‐type star G-­‐type star M-­‐type star It depends on rota0on but also on mass (convec0on zone depth). 5. Stellar maps They allow us to derive the spot area, distribu0on, temperature and their 0me varia0ons Lanza et al. 2009, A&A 493, 193 PLATO data Will be very valuable for the rota0onal studies. The work package WP123500 will get ready the “tools to measure rota0onal modula0on” The advantages of PLATO data with respect to ground-­‐based data are:   High photometric accuracy  detec0on of very low variability levels and extension of our analysis to very slow rotators   Uninterrupted 0meseries and high 0me resolu0on  no aliasing  all variability 0mescales accessible   High number of monitored targets  robust sta0s0cs , accurate rela0ons between period, magne0c ac0city, and basic stellar parameters (from asteroseismology, Gaia data, and ground-­‐based spectroscopy)