Vera Wolthoff (Germany)
vwolthoff @ lsw.uni-heidelberg.de
Evolution of Planetary Systems on the Giant Branch
With the growing number of exoplanets detected around evolved stars, it becomes evident that the planet population around giant stars possesses different properties than the population around main-sequence stars; most notably, close-in planets seem to be very rare, while being abundant around main-sequence stars.
As giant star Doppler surveys sample larger stellar masses than their main-sequence counterpart, the differences could be primordial with close-in planets (a <∼ 0.5 AU) not forming around higher mass stars in the first place (due to faster disk depletion, longer migration timescale, and a more distant snow line). On the other hand, the stellar post-main-sequence evolution can alter planetary systems and cause engulfment of close-in planets.
We study the effect of stellar evolution on the orbital architecture by simulating the combined effects of tidally induced orbital decay and mass loss induced orbital expansion on the semi-major axes of a number of planets detected around evolved stars. Running our simulations backwards in time allows us to determine the orbital configuration on the main-sequence and to compare it to the observed planet population around less massive main-sequence stars. If the simulations cannot reconcile the differences, we will maximize the considered effects using a wider range of input parameters and/or include additional mechanisms.
Furthermore, we will develop a set of criteria for secure planet detection around evolved stars and use it to classify the discovered planets according to their credibility. This will allow us to derive a proper statistical distribution of orbital parameters which then serves as an input to our simulations.
Supervisor: Sabine Reffert (LSW)