A Stellar-mass-dependent Drop in Planet Occurrence Rates

The Kepler Space Telescope has discovered a large number of planets up to one year periods and down to terrestrial sizes.

The cool star subsample allows characterization of small planets near the habitable zone, yet it is not clear if this population is representative of that around sun-like stars. In this paper, we show that occurrence rates of planets around M, K, G, and F stars observed with Kepler are significantly different from each other. We identify two trends with stellar mass: First, the occurrence of Earth to Neptune-sized planets (1 to 4 Earth radii) is successively higher towards cooler stars at all orbital periods probed by Kepler, confirming the result of Howard et al. (2012) and extending it down to Earth-sized planets; Second, a drop in occurrence rates towards the star is evident for all spectral types inwards of a ~10 day orbital period, with a plateau further out.

The distance from the star where this drop occurs depends on spectral type, and scales with semi-major axis as the cube root of stellar mass. By comparing different mechanisms of planet formation, trapping and destruction, we find that this scaling best matches the location of the pre-main-sequence co-rotation radius, indicating efficient trapping of migrating planets or planetary building blocks close to the star. These results demonstrate the stellar-mass dependence of the planet population — both in terms of occurence rate and of orbital distribution. The prominent stellar-mass dependence of the inner boundary of the planet population shows that the formation or migration of planets is sensitive to the stellar parameters.

Gijs D. Mulders, Ilaria Pascucci, Daniel Apai (Submitted on 28 Jun 2014)

Comments: 18 pages, 7 figures

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Cite as: arXiv:1406.7356 [astro-ph.EP] (or arXiv:1406.7356v1 [astro-ph.EP] for this version)

Submission history From: Gijs Mulders [v1] Sat, 28 Jun 2014 05:00:21 GMT (849kb,D)