Precise Masses in the WASP-47 System

Andrew Vanderburg, Juliette C. Becker, Lars A. Buchhave, Annelies Mortier, Eric Lopez, Luca Malavolta, Raphaëlle D. Haywood, David W. Latham, David Charbonneau, Mercedes López-Morales, Fred C. Adams, Aldo Stefano Bonomo, François Bouchy, Andrew Collier Cameron, Rosario Cosentino, Luca Di Fabrizio, Xavier Dumusque, Aldo F. M. Fiorenzano, Avet Harutyunyan, John Asher JohnsonVania Lorenzi, Christophe Lovis, Michel Mayor, Giusi Micela, Emilio Molinari, Marco Pedani, Francesco Pepe, Giampaolo Piotto, David F. Phillips, Ken Rice, Dimitar Sasselov, Damien Ségransan, Alessandro Sozzetti, Stéphane Udry, Chris Watson

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Abstract

We present precise radial velocity observations of WASP-47, a star known to host a hot Jupiter, a distant Jovian companion, and, uniquely, two additional transiting planets in short-period orbits: a super-Earth in a ~19 hour orbit, and a Neptune in a ~9 day orbit. We analyze our observations from the HARPS-N spectrograph along with previously published data to measure the most precise planet masses yet for this system. When combined with new stellar parameters and reanalyzed transit photometry, our mass measurements place strong constraints on the compositions of the two small planets. We find unlike most other ultra-short-period planets, the inner planet, WASP-47 e, has a mass (6.83 +/- 0.66 Me) and radius (1.810 +/- 0.027 Re) inconsistent with an Earth-like composition. Instead, WASP-47 e likely has a volatile-rich envelope surrounding an Earth-like core and mantle. We also perform a dynamical analysis to constrain the orbital inclination of WASP-47 c, the outer Jovian planet. This planet likely orbits close to the plane of the inner three planets, suggesting a quiet dynamical history for the system. Our dynamical constraints also imply that WASP-47 c is much more likely to transit than a geometric calculation would suggest. We calculate a transit probability for WASP-47 c of about 10%, more than an order of magnitude larger than the geometric transit probability of 0.6%.
Original languageEnglish
Number of pages14
JournalAstronomical Journal
Volume154
Issue number6
Early online date17 Nov 2017
DOIs
Publication statusPublished - Dec 2017

Bibliographical note

15 pages, 3 figures, 3 tables. Accepted in AJ

Keywords

  • astro-ph.EP

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