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arXiv · 1501.01305

Kepler-445, Kepler-446 and the Occurrence of Compact Multiples Orbiting Mid-M Dwarf Stars

Philip S. Muirhead·Andrew W. Mann·Andrew Vanderburg·Timothy D. Morton·Adam Kraus·Michael Ireland·Jonathan J. Swift·Gregory A. Feiden·Eric Gaidos·J. Zachary Gazak
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Abstract

We confirm and characterize the exoplanetary systems Kepler-445 and Kepler-446: two mid-M dwarf stars, each with multiple, small, short-period transiting planets. Kepler-445 is a metal-rich ([Fe/H]=+0.25 $\pm$ 0.10) M4 dwarf with three transiting planets, and Kepler-446 is a metal-poor ([Fe/H]=-0.30 $\pm$ 0.10) M4 dwarf also with three transiting planets. Kepler-445c is similar to GJ 1214b: both in planetary radius and the properties of the host star. The Kepler-446 system is similar to the Kepler-42 system: both are metal-poor with large galactic space velocities and three short-period, likely-rocky transiting planets that were initially assigned erroneously large planet-to-star radius ratios. We independently determined stellar parameters from spectroscopy and searched for and fitted the transit light curves for the planets, imposing a strict prior on stellar density in order to remove correlations between the fitted impact parameter and planet-to-star radius ratio for short-duration transits. Combining Kepler-445, Kepler-446 and Kepler-42, and isolating all mid-M dwarf stars observed by Kepler with the precision necessary to detect similar systems, we calculate that 21 $^{+7}_{-5}$ % of mid-M dwarf stars host compact multiples (multiple planets with periods of less than 10 days) for a wide range of metallicities. We suggest that the inferred planet masses for these systems support highly efficient accretion of protoplanetary disk metals by mid-M dwarf protoplanets.

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Philip S. Muirhead, Andrew W. Mann, Andrew Vanderburg, Timothy D. Morton, Adam Kraus, Michael Ireland, Jonathan J. Swift, Gregory A. Feiden, Eric Gaidos, J. Zachary Gazak. 2015-01-06. Kepler-445, Kepler-446 and the Occurrence of Compact Multiples Orbiting Mid-M Dwarf Stars. https://doi.org/10.1088/0004-637x%2F801%2F1%2F18

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