Characterization of Low-mass K2 Planet Hosts Using Near-infrared Spectroscopy

We present moderate resolution near-infrared spectra in the H, J, and K band of M-dwarf hosts to candidate transiting exoplanets discovered by NASA’s K2 mission. We employ known empirical relationships between spectral features and physical stellar properties to measure the effective temperature, radius, metallicity, and luminosity of our sample.

Out of an initial sample of 56 late-type stars in K2, we identify 35 objects as M dwarfs. For that subsample, we derive temperatures ranging from 2870 to 4187 K, radii of 0.09–0.83 R⊙, luminosities of -2.67 < log L/L , < -0.67 and [Fe/H] metallicities between −0.49 and 0.51 dex. We then employ the stellar properties derived from spectra, in tandem with the K2 light curves, to characterize their planets.

We report 33 exoplanet candidates with orbital periods ranging from 0.19 to 21.16 days, and median radii and equilibrium temperatures of 2.3 R⊕ and 986 K, respectively. Using planet mass–radius relationships from the literature, we identify seven exoplanets as potentially rocky, although we conclude that probably none reside in the habitable zone of their parent stars.