Probing the surfaces of Sun-like stars using transiting planets and 3D magneto-hydro-dynamical simulations

Mittwoch, 27. Juni 2018, 14:00 - 15:30
Veranstaltungsort* Bibliothek
 Our ability to spatially resolve and visually inspect the solar surface makes the Sun the best studied star to date. Even so, the intricacies of many surface phenomena are poorly understood, especially once we move beyond the Sun. Not only will this prevent us from confirming Earth-like planets, but it also limits many areas of stellar physics, such as dynamo theories. In this talk, I will present a new technique to use transiting planets as probes to spatially resolve stellar spectra. With this, we can inspect centre-to-limb variations in the local absorption line profiles shape and net velocity. In turn, this allows us to search for signatures of magnetic activity (e.g. magneto-convection, spots, faculae) and surface differential rotation (as well as determine the star-planet alignment). It also means that, for the first time, we can make detailed comparisons with 3D magnetohydrodynamical simulations of main-sequence stars other than the Sun. We have successfully applied this technique to a G, K, and M dwarf (WASP-8, HD189733, GJ436); for our brightest target, HD189733, we can detect significant differential rotation and confirm good agreement with MHD simulations. For the Sun, we can make more precise centre-to-limb comparisons, and examine the impact of the magnetic field on convective variations. I will also demonstrate how we can use the sophisticated 3D magneto-hydro-dynamical simulations to understand and predict the relationship between convection-induced line profile shape variations and radial velocities. 

: Dr. Heather Cegla (University of Geneva)