Title: 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.