The star spots of GJ1214 and their application for a lower limit on the spin-orbit alignment
In this talk, I present our photometric effort to learn about the star spots of the super-Earth host star GJ1214 and how we used the starspot tracking technique to derive indications for a spin-orbit misalignment of this star-planet system.
We monitored GJ1214 photometrically for 6 seasons and derived the stellar rotation period, the spot temperature contrast and a permanent spot filling factor. Using the star spot maps calculated by a light curve inversion, we estimate a mean and maximum modification effect on the planetary transmission spectrum by these spots. We find no indications for bright regions on the star.
In the season 2017, we run a large campaign to observe as many transit light curves of GJ1214b as possible during the predicted time of stellar brightness minimum. The brightness minimum means a maximum on spot filling factor and potentially also a maximized number of observed star spot crossings. We aimed at using the star spot occultations in subsequent transits to derive the so far unknown value of the spin-orbit alignment of the super-Earth GJ1214b. We observed a handful of star spot crossing events and do not find them to repeat in subsequent transits. This is a strong indication for a misalignment between stellar spin axis and planetary orbit. GJ1214b is one of the smallest objects with a derivation of this quantity.