HAT-TR-318-007: A Double-lined M Dwarf Binary with Total Secondary Eclipses Discovered by HATNet and Observed by K2

摘要

We report the discovery by the HATNet survey of HAT TR-318-007, a P = 3.34395390 ? 0.00000020 day period detached double-lined M dwarf binary with total secondary eclipses. We combine radial velocity (RV) measurements from TRES/FLWO?1.5 m and time series photometry from HATNet, FLWO?1.2 m, BOS?0.8 m, and NASA K2 Campaign 5, to determine the masses and radii of the component stars: MA 0.448 0.011=N?,MB 0.2721 0.0042= 0.0041?N - +?, RA 0.4548 0.0036= 0.0035?N - + ?, and RB 0.2913 0.0024= 0.0023?N - +. We obtained a FIRE/Magellan near-infrared spectrum of the primary star during a total secondary eclipse, and we use this to obtain disentangled spectra of both components. We determine spectral types of STA = M3.71 0.69 and STB = M5.01 0.73 and effective temperatures of Teff,A = 3190 ? 110 K and Teff,B = 3100 ? 110 K for the primary and secondary star, respectively. We also measure a metallicity of [Fe/H]= +0.298 ? 0.080 for the system. We find that the system has a small, but significant, nonzero eccentricity of 0.0136 ? 0.0026. The K2 light curve shows a coherent variation at a period of 3.41315 0.00032 0.00030 - + days, which is slightly longer than the orbital period, and which we demonstrate comes from the primary star. We interpret this as the rotation period of the primary. We perform a quantitative comparison between the Dartmouth stellar evolution models and the seven systems, including HATTR- 318-007, that contain M dwarfs with 0.2??N < M < 0.5??N, have metallicity measurements, and have masses and radii determined to better than 5% precision. Discrepancies between the predicted and observed masses and radii are found for three of the systems.