SPECTRO-THERMOMETRY OF M DWARFS AND THEIR CANDIDATE PLANETS: TOO HOT, TOO COOL, OR JUST RIGHT?

Abstract

We use moderate-resolution spectra of nearby late K and M dwarf stars with\nparallaxes and interferometrically determined radii to refine their effective\ntemperatures, luminosities, and metallicities. We use these revised values to\ncalibrate spectroscopic techniques to infer the fundamental parameters of more\ndistant late-type dwarf stars. We demonstrate that, after masking out poorly\nmodeled regions, the newest version of the PHOENIX atmosphere models accurately\nreproduce temperatures derived bolometrically. We apply methods to late-type\nhosts of transiting planet candidates in the Kepler field, and calculate\neffective temperature, radius, mass, and luminosity with typical errors of 57\nK, 7%, 11%, and 13%, respectively. We find systematic offsets between our\nvalues and those from previous analyses of the same stars, which we attribute\nto differences in atmospheric models utilized for each study. We investigate\nwhich of the planets in this sample are likely to orbit in the circumstellar\nhabitable zone. We determine that four candidate planets (KOI 854.01, 1298.02,\n1686.01, and 2992.01) are inside of or within 1-sigma of a conservative\ndefinition of the habitable zone, but that several planets identified by\nprevious analyses are not (e.g. KOI 1422.02 and KOI 2626.01). Only one of the\nfour habitable-zone planets is Earth sized, suggesting a downward revision in\nthe occurrence of such planets around M dwarfs. These findings highlight the\nimportance of measuring accurate stellar parameters when deriving parameters of\ntheir orbiting planets.\n