Starspot signature on the light curve: learning about the spot distribution
Ângela Santos (Instituto de Astrofísica e Ciências do Espaço, U.Porto), M. S. Cunha (Instituto de Astrofísica e Ciências do Espaço), P. P. Avelino (Instituto de Astrofísica e Ciências do Espaço), S. Mathur (Space Science Institute), R. A. García (CEA Saclay)

Starspots are cooler/darker than the stellar surface. Therefore, the total flux of a star changes when spots are visible on its surface. The presence of spots together with the stellar rotation leads to a periodic modulation on the light curve. By studying that modulation one can then learn about the stellar rotation and also magnetic activity. Recently, Reinhold & Arlt (2015) proposed a method based on the analysis of the Lomb Scargle Periodogram (LSP) of the light curve to identify the sign of the differential rotation, i.e. weather the equator rotates faster than the poles or the opposite. In this work, we study in detail the spots’ impact on the light curve and on the resulting LSP. We find that, under some conditions, the LSP can actually provide an estimate of the true spot latitudes and/or the stellar inclination angle. Moreover, we find that the impact of the spot on the ratio between the heights of the second and first harmonics of the main peaks in the LSP can be described by a single parameter, the visibility time of the spot. Finally, we also identify possible sources of false positives/negatives for the sign of the differential rotation.