Poster Abstracts

Name/Affiliation:  Xavier Dumusque (Harvard Smithsonian Center for Astrophysics)

Title:  Activity of quiet stars reveals their inclination

Abstract:
Stellar activity, even in quiet stars, is an important limitation to very high precision radial velocity (RV) measurements, which complicates the detection of small mass planets. However activity gives us some important information on stars: activity level, rotational period, presence of differential rotation, presence of magnetic cycles, age with gyrochronology. I will show with this presentation that modeling activity can give us the inclination of the star relative to the line of sight. Several active region simulations have tried to reproduce the variation seen in RVs. These models, assuming dark spots, are successful to explain the RV variation seen on active stars, however cannot explain the modulation seen on quiet stars where plages are dominating. In addition, in these simulations, degeneracy exists between active region latitude and stellar inclination, making it impossible to access to one of these parameters independently. With a new model to simulate the RV effect of spot and plages, based on solar spectra, we manage to reproduce the variation that is observed on HD189733 (spot dominated) and Alpha Centauri B (plage dominated). A good match is observed for the RV variation, but also for others parameters of the cross correlation function such as the bisector span (BIS) and the FWHM. Modeling these three parameters at the same time and comparing with observations allows us to strongly reduce the degeneracy between latitude and inclination, and therefore to measure stellar inclination. Stellar inclination angle with a precision of 20 degrees can be measured and even better if simultaneous photometry exists. This will allow us, without any Rossiter McLauglhin measurement, to calculate the spin orbit angle of transiting planets, and also, assuming a spin orbiting alignment, the true mass of non-transiting planets only detected with RVs.