Exoplanet Demographics versus Host Star Mass: Clues to Formation from Direct Imaging

Michael Meyer (University of Michigan)

The distribution of planetary companion masses, as well as the integrated surface density of companions over fixed mass ranges provide a wealth of information concerning planet formation processes and subsequent dynamical evolution of planetary systems. However, decoding this information requires large samples of host stars of differing mass. Here I will review recent direct imaging results targeting Sun-like FGK stars (e.g. Reggiani et al. 2016; Vigan et al. submitted) combining predictions for planetary mass distributions as well as very low mass brown dwarf binaries suggesting a local minimum in the companion mass ratio distribution. I will also present the latest results from the on-going “next generation” SPHERE SHINE imaging survey on the ESO VLT probing the frequency of gas giant planets on wide orbits. Next I will describe a new model that fits constraints on the surface density distribution of gas giant planets surrounding M dwarfs combining results from radial velocity, microlensing, and imaging surveys (Meyer et al. in press). Finally, I will discuss the implications of these results (the local minima in the companion mass ratio and the local maxima in derived surface density distribution of gas giant companions) as a function of stellar mass. New surveys that can be undertaken with current facilities, the soon to be launched JWST, and instruments yet to be developed, could break model degeneracies and illuminate the role of stellar mass (and thus circumstellar environment) in the planet formation process.

Tuesday, 3 October 2017