Concepedia

They are small worlds after all: revised properties of<i>Kepler</i>M dwarf stars and their planets

Eric Gaidos, Andrew W. Mann, Adam L. Kraus, Michael Ireland

Monthly Notices of the Royal Astronomical Society · 2016 · 203 citations · 122 references

Open access

Abstract

We classified the reddest (r-J > 2.2) stars observed by the NASA Kepler\nmission into main sequence dwarf or evolved giant stars and determined the\nproperties of 4216 M dwarfs based on a comparison of available photometry with\nthat of nearby calibrator stars, as well as available proper motions and\nspectra. We revised the properties of candidate transiting planets using the\nstellar parameters, high-resolution imaging to identify companion stars, and,\nin the case of binaries, fitting light curves to identify the likely planet\nhost. In 49 of 54 systems we validated the primary as the host star. We\ninferred the intrinsic distribution of M dwarf planets using the method of\niterative Monte Carlo simulation. We compared several models of planet orbital\ngeometry and clustering and found that one where planets are exponentially\ndistributed and almost precisely coplanar best describes the distribution of\nmultiplanet systems. We determined that Kepler M dwarfs host an average of\n2.2 ± 0.3 planets with radii of 1-4R ⊕ and orbital periods of\n1.5-180 d. The radius distribution peaks at ~1.2R⊕ and is\nessentially zero at 4R⊕, although we identify three giant planet\ncandidates other than the previously confirmed Kepler-45b. There is suggestive\nbut not significant evidence that the radius distribution varies with orbital\nperiod. The distribution with logarithmic orbital period is flat except for a\ndecline for orbits less than a few days. Twelve candidate planets, including\ntwo Jupiter-size objects, experience an irradiance below the threshold level\nfor a runaway greenhouse on an Earth-like planet and are thus in a "habitable\nzone".