* Astronomy

Title: Characterising the Cool KOIs II. The M Dwarf KOI-254 and its Hot Jupiter
Authors: John Asher Johnson, J. Zachary Gazak, Kevin Apps, Philip S. Muirhead, Justin R. Crepp, Ian J. M. Crossfield, Tabetha Boyajian, Kaspar von Braun, Barbara Rojas-Ayala, Andrew W. Howard, Kevin R. Covey, Everett Schlawin, Katherine Hamren, Timothy D. Morton, James P. Lloyd

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 colours. We use this technique to measure the physical properties of KOI-254 and its planet. We measure a planet mass of Mp = 0.505 Jupiter masses, radius Rp = 0.96 Jupiter radii and semimajor axis a = 0.03 AU, based on our measured stellar mass Mstar = 0.59 Solar masses and radius Rstar = 0.55 Solar radii. We also find that the host star is metal-rich, which is consistent with the sample of M-type stars known to harbour giant planets.

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