%0 Journal Article
%T Characterizing the Cool KOIs III. KOI-961: A Small Star with Large Proper Motion and Three Small Planets
%A Philip S. Muirhead
%A John Asher Johnson
%A Kevin Apps
%A Joshua A. Carter
%A Timothy D. Morton
%A Daniel C. Fabrycky
%A J. Sebastian Pineda
%A Michael Bottom
%A Barbara Rojas-Ayala
%A Everett Schlawin
%A Katherine Hamren
%A Kevin R. Covey
%A Justin R. Crepp
%A Keivan G. Stassun
%A Joshua Pepper
%A Leslie Hebb
%A Evan N. Kirby
%A Andrew W. Howard
%A Howard T. Isaacson
%A Geoffrey W. Marcy
%A David Levitan
%A Tanio Diaz-Santos
%A Lee Armus
%A James P. Lloyd
%J Physics
%D 2012
%I arXiv
%R 10.1088/0004-637X/747/2/144
%X We present the characterization of the star KOI 961, an M dwarf with transit signals indicative of three short-period exoplanets, originally discovered by the Kepler Mission. We proceed by comparing KOI 961 to Barnard's Star, a nearby, well-characterized mid-M dwarf. By comparing colors, optical and near-infrared spectra, we find remarkable agreement between the two, implying similar effective temperatures and metallicities. Both are metal-poor compared to the Solar neighborhood, have low projected rotational velocity, high absolute radial velocity, large proper motion and no quiescent H-alpha emission--all of which is consistent with being old M dwarfs. We combine empirical measurements of Barnard's Star and expectations from evolutionary isochrones to estimate KOI 961's mass (0.13 +/- 0.05 Msun), radius (0.17 +/- 0.04 Rsun) and luminosity (2.40 x 10^(-3.0 +/- 0.3) Lsun). We calculate KOI 961's distance (38.7 +/- 6.3 pc) and space motions, which, like Barnard's Star, are consistent with a high scale-height population in the Milky Way. We perform an independent multi-transit fit to the public Kepler light curve and significantly revise the transit parameters for the three planets. We calculate the false-positive probability for each planet-candidate, and find a less than 1% chance that any one of the transiting signals is due to a background or hierarchical eclipsing binary, validating the planetary nature of the transits. The best-fitting radii for all three planets are less than 1 Rearth, with KOI 961.03 being Mars-sized (Rp = 0.57 +/- 0.18 Rearth), and they represent some of the smallest exoplanets detected to date.
%U http://arxiv.org/abs/1201.2189v1