K2-288Bb: A Small Temperate Planet in a Low-mass Binary System Discovered by Citizen Scientists

Creators: Feinstein, Adina D.; Schlieder, Joshua E.; Livingston, John H.; Ciardi, David R.; Howard, Andrew W.; Arnold, Lauren; Barentsen, Geert; Bristow, Makennah; Christiansen, Jessie L.; Crossfield, Ian J. M.; Dressing, Courtney D.; Gonzales, Erica J.; Kosiarek, Molly; Lintott, Chris J.; Miller, Grant; Morales, Farisa Y.; Petigura, Erik A.; Thackeray, Beverly; Ault, Joanne; Baeten, Elisabeth; Jonkeren, Alexander F.; Langley, James; Moshinaly, Houssen; Pearson, Kirk; Tanner, Christopher; Treasure, Joanna

Abstract

Observations from the Kepler and K2 missions have provided the astronomical community with unprecedented amounts of data to search for transiting exoplanets and other astrophysical phenomena. Here, we present K2-288, a low-mass binary system (M2.0 ± 1.0; M3.0 ± 1.0) hosting a small (R_p = 1.9 R⊕), temperate (T_(eq) = 226 K) planet observed in K2 Campaign 4. The candidate was first identified by citizen scientists using Exoplanet Explorers hosted on the Zooniverse platform. Follow-up observations and detailed analyses validate the planet and indicate that it likely orbits the secondary star on a 31.39-day period. This orbit places K2-288Bb in or near the habitable zone of its low-mass host star. K2-288Bb resides in a system with a unique architecture, as it orbits at >0.1 au from one component in a moderate separation binary (a_(proj) ~ 55 au), and further follow-up may provide insight into its formation and evolution. Additionally, its estimated size straddles the observed gap in the planet radius distribution. Planets of this size occur less frequently and may be in a transient phase of radius evolution. K2-288 is the third transiting planet system identified by the Exoplanet Explorers program and its discovery exemplifies the value of citizen science in the era of Kepler, K2, and the Transiting Exoplanet Survey Satellite.

Additional Information

© 2019 The American Astronomical Society. Received 2018 August 31; revised 2018 December 18; accepted 2018 December 19; published 2019 January 7. We would like to acknowledge all other citizen scientists who were directly involved in flagging this system as well as those who continue to do so. This work, and hopefully many more in the future, was made possible by the Exoplanet Explorers project hosted on Zooniverse.org. Based on the responses from those citizen scientists who are credited as authors here, we encourage the practice of science teams reaching out to citizen scientists for all future discovery papers. We would additionally like to thank our anonymous referee for taking the time to review our report in great detail, which created a more complete picture of the system presented here. 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. M.B. acknowledges support from the North Carolina Space Grant Consortium. L.A. acknowledges support from NASA's Minority University Research and Education Program Institutional Research Opportunity to the University of the Virgin Islands. E.J.G. acknowledges support from the NSF graduate research fellowship program. M.R.K. acknowledges support from the NSF Graduate Research Fellowship, grant No. DGE 1339067. B.T. acknowledges support from the National Science Foundation Graduate Research Fellowship under grant number DGE1322106 and NASAs Minority University Research and Education Program. This work made use of the SIMBAD database (operated at CDS, Strasbourg, France); NASA's Astrophysics Data System Bibliographic Services; NASA's Exoplanet Archive and Infrared Science Archive; data products from the Two Micron All Sky Survey (2MASS); the APASS database; the Digitized Sky Survey; and the Wide-Field Infrared Survey Explorer (WISE). This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. 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. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: IRTF:3.0m (SpeX) - , Keck:I (HIRES) - , Keck:II (NIRC2) - , Kepler - , Spitzer. - Software: k2phot (Petigura et al. 2015), TERRA (Petigura et al. 2013a, 2013b), EVEREST (Luger et al. 2018), emcee (Foreman-Mackey et al. 2013), batman (Kreidberg 2015), vespa (Morton 2015).

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