Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars I: Classifying Low-mass Host Stars Observed During Campaigns 1-7

Abstract

We present near-infrared spectra for 144 candidate planetary systems identified during Campaigns 1-7 of the NASA K2 Mission. The goal of the survey was to characterize planets orbiting low-mass stars, but our IRTF/SpeX and Palomar/TripleSpec spectroscopic observations revealed that 49% of our targets were actually giant stars or hotter dwarfs reddened by interstellar extinction. For the 72 stars with spectra consistent with classification as cool dwarfs (spectral types K3 - M4), we refined their stellar properties by applying empirical relations based on stars with interferometric radius measurements. Although our revised temperatures are generally consistent with those reported in the Ecliptic Plane Input Catalog (EPIC), our revised stellar radii are typically 0.13 solar radii (39%) larger than the EPIC values, which were based on model isochrones that have been shown to underestimate the radii of cool dwarfs. Our improved stellar characterizations will enable more efficient prioritization of K2 targets for follow-up studies.

36 pages, 25 figures, 7 tables, in press at ApJ. Stellar parameters and spectra posted to ExoFOP-K2 (https://exofop.ipac.caltech.edu/k2/). Also see related paper by Martinez et al. titled "Stellar & Planetary Parameters for K2's Late Type Dwarf Systems from C1 to C5."

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Cited by in corpus (7)

• Zodiacal Exoplanets in Time (ZEIT) VI: a three-planet system in the Hyades cluster including an Earth-sized planet
• Precise Masses in the WASP-47 System
• Planet Candidates from K2 Campaigns 5-8 and Follow-Up Optical Spectroscopy
• Simulating the Exoplanet Yield of a Space-based MIR Interferometer Based on Kepler Statistics
• Stellar & Planetary Parameters for K2's Late Type Dwarf Systems from C1 to C5
• The Gold Standard: Accurate Stellar and Planetary Parameters for Eight Kepler M dwarf Systems Enabled by Parallaxes
• K2-288Bb: A Small Temperate Planet in a Low-mass Binary System Discovered by Citizen Scientists