Three's Company: An additional non-transiting super-Earth in the bright HD 3167 system, and masses for all three planets

Creators: Christiansen, Jessie L.; Ciardi, David R.; Fulton, B. J.; Howard, Andrew W.; Sinukoff, Evan; Batygin, Konstantin; Benneke, Björn; Dressing, Courtney; Knutson, Heather A.; Petigura, Erik

Abstract

HD 3167 is a bright (V = 8.9), nearby K0 star observed by the NASA K2 mission (EPIC 220383386), hosting two small, short-period transiting planets. Here we present the results of a multi-site, multi-instrument radial-velocity campaign to characterize the HD 3167 system. The masses of the transiting planets are 5.02 ± 0.38 M⊕ for HD 3167 b, a hot super-Earth with a likely rocky composition (ρ_b = 5.60^(+2.15)_(-1.43) g cm^(−3)), and 9.80^(+1.30)_(-1.24) M⊕ for HD 3167 c, a warm sub-Neptune with a likely substantial volatile complement (ρ_c = 1.97^(+0.94)_(0.59) g cm^(−3)). We explore the possibility of atmospheric composition analysis and determine that planet c is amenable to transmission spectroscopy measurements, and planet b is a potential thermal emission target. We detect a third, non-transiting planet, HD 3167 d, with a period of 8.509 ± 0.045 d (between planets b and c) and a minimum mass of 6.90 ± 0.71 M⊕. We are able to constrain the mutual inclination of planet d with planets b and c: we rule out mutual inclinations below 1 3 because we do not observe transits of planet d. From 1 3 to 40°, there are viewing geometries invoking special nodal configurations, which result in planet d not transiting some fraction of the time. From 40° to 60°, Kozai–Lidov oscillations increase the system's instability, but it can remain stable for up to 100 Myr. Above 60°, the system is unstable. HD 3167 promises to be a fruitful system for further study and a preview of the many exciting systems expected from the upcoming NASA TESS mission.

Additional Information

© 2017 The American Astronomical Society. Received 2017 March 3; revised 2017 April 25; accepted 2017 April 28; published 2017 August 31. This paper and the paper by Gandolfi et al. were prepared simultaneously and are the result of independent radial-velocity observations and analyses of the HD 3167 system. We thank the HARPS team for their collegiality. We also thank the many observers who contributed to the measurements reported here. We thank Kyle Lanclos, Matt Radovan, Will Deich, and the rest of the UCO Lick staff for their invaluable help shepherding, planning, and executing observations, in addition to writing the low-level software that made the automated APF observations possible. We are grateful to the time assignment committees of the University of Hawai'i, the University of California, and NASA for their generous allocations of observing time. 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 material is based upon work supported by the National Science Foundation Graduate Research Fellowship under grant No. 2014184874. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation. The research leading to these results has received funding from the European Union Seventh Framework Program (FP7/2007–2013) under grant agreement number 313014 (ETAEARTH). This publication was made possible through the support of a grant from the John Templeton Foundation. The opinions expressed are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. This material is based upon work supported by NASA under grant Nos. NNX15AC90G and NNX17AB59G issued through the Exoplanets Research Program. 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. This research has also 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. This research has made use of the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The Digitized Sky Survey was produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. This research has made use of the NASA Exoplanet Follow-Up Observation Program website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Finally, the authors wish to extend special thanks to those of Hawai'ian ancestry on whose sacred mountain of Maunakea we are privileged to be guests. Without their generous hospitality, the Keck observations presented herein would not have been possible. Facilities: Kepler - The Kepler Mission, Keck(HIRES - , NIRC2) - , APF - , TNG - Telescopio Nazionale Galileo. Software: emcee (Foreman-Mackey et al. 2013), isochrones (Morton 2015), RadVel (Fulton & Petigura 2017, in preparation).

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