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Surface rotation and photometric activity of Kepler solar-type stars

Dr. Angela Santos
Space Science Institute

June 25th, 2019


Brightness variations due to dark spots on the stellar surface encode information about stellar surface rotation and magnetic activity. As stars slow down and become less active, the rotation rate is observed to decrease, thus rotation is often used as a diagnostic for age. Rotation and magnetic fields affect stellar evolution and the mode frequencies used to infer fundamental properties of stars. Furthermore, rotation itself is an important ingredient for dynamo mechanisms. Therefore, it is of extreme importance to constrain surface rotation and magnetic properties of stars. In this work, we analyze the spot modulation in light-curves for main-sequence and subgiant stars observed by Kepler main-mission. We analyze four data sets: KADACS time-series obtained for 20-, 55-, and 80-day filters; and PDC-MAP time-series. The rotation estimates are retrieved through a combination of wavelet analysis and the autocorrelation function of light-curves. Reliable rotation periods are determined by comparing the rotation estimates obtained from the different diagnostics and for the different time-series. We recover rotation periods for more than 60% of the targets. For those, we also study the photometric activity level and lifetime of active regions. We find the rotation rate to increase with effective temperature and mass, while the photometric activity proxy increases towards fast rotators. Active region lifetimes are found to be longer with increasing rotation rate and photometric activity. In this analysis we also identify potential polluters, such as mis-classified Red Giants, classical pulsator candidates, and photometric pollution of light-curves.