Mass Constraints of the WASP-47 Planetary System from Radial Velocities

Creators: Sinukoff, Evan; Howard, Andrew W.; Petigura, Erik A.; Fulton, Benjamin J.; Isaacson, Howard; Weiss, Lauren M.; Brewer, John M.; Hansen, Brad M. S.; Hirsch, Lea; Christiansen, Jessie L.; Crepp, Justin R.; Crossfield, Ian J. M.; Schlieder, Joshua E.; Ciardi, David R.; Beichman, Charles A.; Knutson, Heather A.; Benneke, Bjoern; Dressing, Courtney D.; Livingston, John H.; Deck, Katherine M.; Lépine, Sébastien; Rogers, Leslie A.

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Abstract

We report precise radial velocity (RV) measurements of WASP-47, a G star that hosts three transiting planets in close proximity (a hot Jupiter, a super-Earth, and a Neptune-sized planet) and a non-transiting planet at 1.4 au. Through a joint analysis of previously published RVs and our own Keck-HIRES RVs, we significantly improve the planet mass and bulk density measurements. For the super-Earth WASP-47e (P = 0.79 days), we measure a mass of 9.11 ± 1.17 M_⊕, and a bulk density of 7.63 ± 1.90 g cm^(−3), consistent with a rocky composition. For the hot Jupiter WASP-47b (P = 4.2 days), we measure a mass of 356 ± 12 M_⊕ (1.12 ± 0.04 M_(Jup)) and constrain its eccentricity to $\lt 0.021$ at 3σ confidence. For the Neptune-size planet WASP-47d (P = 9.0 days), we measure a mass of 12.75 ± 2.70 M_⊕ and a bulk density of 1.36 ± 0.42 g cm^(−3), suggesting that it has a thick H/He envelope. For the outer non-transiting planet, we measure a minimum mass of 411 ± 18 M_⊕ (1.29 ± 0.06 M_(Jup)), an orbital period of 595.7 ± 5.0 days, and an orbital eccentricity of 0.27 ± 0.04. Our new measurements are consistent with but two to four times more precise than previous mass measurements.

Additional Information

© 2017. The American Astronomical Society. Received 2016 October 23. Accepted 2016 December 6. Published 2017 January 13. We thank the many observers who contributed to the measurements reported here. We thank Geoff Marcy and Trevor David for helpful discussions. We thank Tom Greene, Michael Werner, Michael Endl, and William Cochrane for participation in our NASA Key Project. We gratefully acknowledge the efforts and dedication of the Keck Observatory staff. This paper includes data collected by the K2 mission. Funding for the K2 mission is provided by the NASA Science Mission directorate. 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. B.J.F. was supported by the National Science Foundation Graduate Research Fellowship under grant No. 2014184874. 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. L.M.W. acknowledges the Trottier Family Foundation for their generous support. 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 the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Finally, the authors 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:I (HIRES)

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