Modeling Starspot Features on a Solar Type Star with an M-dwarf Companion

Understanding magnetic activity on the surface of stars other than the Sun is particularly important for planet hosting stars since exoplanet analyses must include these effects to properly characterize the exoplanet’s atmosphere. Using data from the Kepler spacecraft, we use the starspot modeling program STSP to measure the position and size of spots for KOI-340 (WISE J195039.52+474804.8) which is an eclipsing binary consisting of Solar-type star (M_* = 1.10 ± 0.07 M☉) with an M-dwarf companion (M_* = 0.214 ± 0.006 M☉). STSP uses a novel technique to measure the spot positions and radii by using the transiting secondary as a magnifying glass to probe down to less than 1% changes in the surface brightness of the star for high-precision photometry. Preliminary results show the minimum size of spot features on KOI-340 is 10% the size of the star i.e. two times larger than the size of the majority of Sunspots and Sunspot groups at Solar maximum (Howard et al. 1984). Though KOI-340 has a similar T_eff (5770K) as the Sun, it rotates at a rate of 12.9 days, which is ~2 times faster than the Sun and could be contributing to the larger spots. A similar analysis showed that a K4 dwarf HAT-P-11 has similar size spots as the Sun, but there are ~100 times more of them (Morris et al. 2017). This analysis is part of a larger program to characterize starspot properties using high-precision transiting exoplanet light curves across a range of spectral types and rotation rates. This research is funded through NSF grants 1907622, 1909506, 1909682, 1910954.