Characterizing the Cool KOIs II. The M Dwarf KOI-254 and its Hot Jupiter

TL;DR

This paper confirms and characterizes KOI-254b, the first hot Jupiter around an M dwarf, using multiple observational techniques and introduces a new photometric method to estimate M dwarf properties.

Contribution

It presents the discovery of the first hot Jupiter orbiting an M dwarf and introduces a novel broadband photometry technique for estimating M dwarf mass and metallicity.

Findings

KOI-254b is a hot Jupiter with 0.505 Mjup mass and 0.96 Rjup radius.

The host star is metal-rich and has a mass of 0.59 Msun.

A new photometric calibration for M dwarf metallicity is developed.

Abstract

We report the confirmation and characterization of a transiting gas giant planet orbiting the M dwarf KOI-254 every 2.455239 days, which was originally discovered by the Kepler mission. We use radial velocity measurements, adaptive optics imaging and near infrared spectroscopy to confirm the planetary nature of the transit events. KOI-254b is the first hot Jupiter discovered around an M-type dwarf star. We also present a new model-independent method of using broadband photometry to estimate the mass and metallicity of an M dwarf without relying on a direct distance measurement. Included in this methodology is a new photometric metallicity calibration based on J-K colors. We use this technique to measure the physical properties of KOI-254 and its planet. We measure a planet mass of Mp = 0.505 Mjup, radius Rp = 0.96 Rjup and semimajor axis a = 0.03 AU, based on our measured stellar mass Mstar = 0.59 Msun and radius Rstar = 0.55 Rsun. We also find that the host star is metal-rich, which is consistent with the sample of M-type stars known to harbor giant planets.