Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. I. Classifying Low-mass Host Stars Observed during Campaigns 1–7
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 Infrared Telescope Facility/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 R_⊙ (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.
Additional Information© 2017. The American Astronomical Society. Received 2016 September 5; revised 2016 November 17; accepted 2016 November 18; published 2017 February 17. Many of our targets were provided by the K2 California Consortium (K2C2). We thank K2C2 for sharing their candidate lists and vetting products. In particular, we thank K2C2 members Ian Crossfield and Arturo Martinez for their willingness to coordinate follow-up observations of low-mass stars. We are grateful to Michael Cushing for sharing a beta version of the Spextool pipeline designed for TripleSpec data. We thank Philip Muirhead and Juliette Becker for providing advice regarding TripleSpec data acquisition and reduction. We also acknowledge helpful conversations with Chas Beichman and Eric Gaidos. We thank Andrew Howard for donating SpeX time and Kimberly Aller, Will Best, and Michael Liu for obtaining some of the SpeX observations described in this paper. Finally, we thank the anonymous referee for providing feedback that improved the quality of this paper. This work was performed under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. This publication was made possible through the support of a grant from the John Templeton Foundation. The opinions expressed here are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. This paper includes data collected by the K2 mission, which is funded by the NASA Science Mission directorate. Our follow-up observations were obtained at the IRTF, which is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration and at Palomar Observatory. We thank the staff at both observatories and the Caltech Remote Observing Facilities staff for supporting us during our many observing runs. We are grateful to the IRTF and Caltech TACs for awarding us telescope time. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: IRTF (SpeX), Palomar (TripleSpec).
Published - Dressing_2017_ApJ_836_167.pdf
Submitted - 1701.00586.pdf