Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation

Creators: Montet, Benjamin T.; Morton, Timothy D.; Foreman-Mackey, Daniel; Johnson, John Asher; Hogg, David W.; Bowler, Brendan P.; Latham, David W.; Bieryla, Allyson; Mann, Andrew W.

Abstract

The extended Kepler mission, K2, is now providing photometry of new fields every three months in a search for transiting planets. In a recent study, Foreman-Mackey and collaborators presented a list of 36 planet candidates orbiting 31 stars in K2 Campaign 1. In this contribution, we present stellar and planetary properties for all systems. We combine ground-based seeing-limited survey data and adaptive optics imaging with an automated transit analysis scheme to validate 21 candidates as planets, 17 for the first time, and identify 6 candidates as likely false positives. Of particular interest is K2-18 (EPIC 201912552), a bright (K = 8.9) M2.8 dwarf hosting a 2.23 ± 0.25 R⊕ planet with T_(eq) = 272 ± 15 K and an orbital period of 33 days. We also present two new open-source software packages which enable this analysis. The first, isochrones, is a flexible tool for fitting theoretical stellar models to observational data to determine stellar properties using a nested sampling scheme to capture the multimodal nature of the posterior distributions of the physical parameters of stars that may plausibly be evolved. The second is vespa, a new general-purpose procedure to calculate false positive probabilities and statistically validate transiting exoplanets.

Additional Information

© 2015 The American Astronomical Society. Received 2015 March 27; accepted 2015 July 2; published 2015 August 5. We thank Roberto Sanchis-Ojeda (Berkeley), Dan Huber (Sydney) and Jeff Coughlin (SETI) for conversations and suggestions which improved the quality of this manuscript. We also thank Keivan Stassun (Vanderbilt) for his insights into stellar parameters and the rate of subgiant contamination for both Kepler and K2, which significantly improved this work. We thank the anonymous referee for their comments and suggestions. We are grateful to the entire Kepler team, past and present. Their tireless efforts were all essential to the tremendous success of the mission and the successes of K2 present and future. Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contracts. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. This paper includes data collected by the Sloan Digital Sky Survey. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, and the U.S. Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration including the University of Arizona, the Brazilian Participation Group, Brookhaven National Laboratory, Carnegie Mellon University, University of Florida, the French Participation Group, the German Participation Group, Harvard University, the Instituto de Astrofisica de Canarias, the Michigan State/Notre Dame/JINA Participation Group, Johns Hopkins University, Lawrence Berkeley National Laboratory, Max Planck Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University, Ohio State University, Pennsylvania State University, University of Portsmouth, Princeton University, the Spanish Participation Group, University of Tokyo, University of Utah, Vanderbilt University, University of Virginia, University of Washington, and Yale University. B.T.M. is supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144469. J.A.J. is supported by generous grants from the David and Lucile Packard Foundation and the Alfred P. Sloan Foundation. D.F.M. and D.W.H. were partially supported by the National Science Foundation (grant IIS-1124794), the National Aeronautics and Space Administration (grant NNX12AI50G), and the Moore-Sloan Data Science Environment at NYU. T.D.M. is supported by the National Aeronautics and Space Administration (grant NNX14AE11G). Facilities: Kepler - The Kepler Mission, Hale(PHARO) -, FLWO:1.5 m -, IRTF(SpeX) - Infrared Telescope Facility

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