Stellar and Planetary Parameters for K2's Late-type Dwarf Systems from C1 to C5
The NASA K2 mission uses photometry to find planets transiting stars of various types. M dwarfs are of high interest since they host more short-period planets than any other type of main-sequence star and transiting planets around M dwarfs have deeper transits compared to other main-sequence stars. In this paper, we present stellar parameters from K and M dwarfs hosting transiting planet candidates discovered by our team. Using the SOFI spectrograph on the European Southern Observatory's New Technology Telescope, we obtained R ≈ 1000 J-, H-, and K-band (0.95–2.52 μm) spectra of 34 late-type K2 planet and candidate planet host systems and 12 bright K4–M5 dwarfs with interferometrically measured radii and effective temperatures. Out of our 34 late-type K2 targets, we identify 27 of these stars as M dwarfs. We measure equivalent widths of spectral features, derive calibration relations using stars with interferometric measurements, and estimate stellar radii, effective temperatures, masses, and luminosities for the K2 planet hosts. Our calibrations provide radii and temperatures with median uncertainties of 0.059 R⊙ (16.09%) and 160 K (4.33%), respectively. We then reassess the radii and equilibrium temperatures of known and candidate planets based on our spectroscopically derived stellar parameters. Since a planet's radius and equilibrium temperature depend on the parameters of its host star, our study provides more precise planetary parameters for planets and candidates orbiting late-type stars observed with K2. We find a median planet radius and an equilibrium temperature of approximately 3 R⊕ and 500 K, respectively, with several systems (K2-18b and K2-72e) receiving near-Earth-like levels of incident irradiation.
Additional Information© 2017 The American Astronomical Society. Received 2016 October 3; revised 2016 December 28; accepted 2017 January 2; published 2017 March 3. A.O.M. would like to thank all of the members of the K2 team for all the assistance and interesting conversations throughout this work. A.W.H. acknowledges support for our K2 team through a NASA Astrophysics Data Analysis Program grant. A.W.H. and I.J.M.C. acknowledge support from the K2 Guest Observer Program. Finally, we thank the anonymous referee for the insightful comments that improved the quality of this manuscript. This material is based on work supported by the National Science Foundation under Award nos. AST-1322432, a PAARE Grant for the California-Arizona Minority Partnership for Astronomy Research and Education (CAMPARE), and DUE-1356133, an S-STEM Grant for the Cal-Bridge CSU-UC PhD Bridge Program. This work was funded in part by Spitzer GO 11026 (PI Werner), managed by JPL/Caltech under a contract with NASA and locally by the University of Arizona. This work was performed in part under contract with the California Institute of Technology/Jet Propulsion Laboratory funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. Travel costs were partially supported by the National Geographic Society. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.
Published - Martinez_2017_ApJ_837_72.pdf
Submitted - 1701.00588.pdf