Spitzer transit follow-up of planet candidates from the K2 mission

Creators: Livingston, John H.; Crossfield, Ian J. M.; Werner, Michael W.; Gorjian, Varoujan; Petigura, Erik A.; Ciardi, David R.; Dressing, Courtney D.; Fulton, Benjamin J.; Hirano, Teruyuki; Schlieder, Joshua E.; Sinukoff, Evan; Kosiarek, Molly; Akeson, Rachel; Beichman, Charles A.; Benneke, Björn; Christiansen, Jessie L.; Hansen, Bradley M. S.; Howard, Andrew W.; Isaacson, Howard; Knutson, Heather A.; Krick, Jessica; Martinez, Arturo O.; Sato, Bun'ei; Tamura, Motohide

Abstract

We present precision 4.5 µm Spitzer transit photometry of eight planet candidates discovered by the K2 mission: K2-52 b, K2-53 b, EPIC 205084841.01, K2-289 b, K2-174 b, K2-87 b, K2-90 b, and K2-124 b. The sample includes four sub-Neptunes and two sub-Saturns, with radii between 2.6 and 18 R⊕ and equilibrium temperatures between 440 and 2000 K. In this paper we identify several targets of potential interest for future characterization studies, demonstrate the utility of transit follow-up observations for planet validation and ephemeris refinement, and present new imaging and spectroscopy data. Our simultaneous analysis of the K2 and Spitzer light curves yields improved estimates of the planet radii and multiwavelength information that helps validate their planetary nature, including the previously unvalidated candidate EPIC 205686202.01 (K2-289 b). Our Spitzerobservations yield an order-of-magnitude increase in ephemeris precision, thus paving the way for efficient future study of these interesting systems by reducing the typical transit timing uncertainty in mid-2021 from several hours to a dozen or so minutes. K2-53 b, K2-289 b, K2-174 b, K2-87 b, and K2-90 b are promising radial velocity (RV) targets given the performance of spectrographs available today or in development, and the M3V star K2-124 hosts a temperate sub-Neptune that is potentially a good target for both RV and atmospheric characterization studies.

Additional Information

© 2019 The American Astronomical Society. Received 2018 March 23; revised 2019 January 8; accepted 2019 January 14; published 2019 February 8. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology (Caltech), under contract with the National Aeronautics and Space Administration (NASA). This paper includes data collected by the K2 mission. Funding for the K2 mission is provided by the NASA Science Mission directorate. This work benefited from the Exoplanet Summer Program in the Other Worlds Laboratory (OWL) at the University of California, Santa Cruz, a program funded by the Heising-Simons Foundation. E.S. is supported by a postgraduate scholarship from the Natural Sciences and Engineering Research Council of Canada. E.A.P. acknowledges support by NASA through a Hubble Fellowship grant awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. 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. This work was performed (in part) under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. This research has made use of the NASA Exoplanet Archive, which is operated by Caltech, under contract with NASA's Exoplanet Exploration Program. This work made use of the SIMBAD database (operated at CDS, Strasbourg, France) and NASA's Astrophysics Data System Bibliographic Services. This research made use of the Infrared Science Archive, which is operated by Caltech, under contract with NASA. Portions of this work were performed at the California Institute of Technology under contract with NASA. Some of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership between Caltech, the University of California, and NASA. The authors wish to extend special thanks to those of Hawai'ian ancestry, on whose sacred mountain of Maunakea we are privileged to be quests. We are most fortunate to have the opportunity to conduct observations from this mountain. Facilities: Kepler - The Kepler Mission, Spitzer - , Gaia - , Keck (NIRC2 - , HIRES) - , Subaru (HDS). - Software: numpy (Oliphant 2006), scipy (Jones et al. 2001), matplotlib (Hunter 2007), lmfit (Newville et al. 2014), emcee (Foreman-Mackey et al. 2013), celerite (Foreman-Mackey et al. 2017), batman (Kreidberg 2015), isochrones (Morton 2015a), vespa, (Morton 2015b), k2phot (Petigura et al. 2015), SpecMatch-syn (Petigura 2015), SpecMatch-emp (Yee et al. 2017b), RadVel (Fulton et al. 2018), IRAF (Tody 1986, 1993).

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