Precise masses in the WASP-47 system
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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 hr 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 transitphotometry, 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 M⊕) and radius (1.810 ± 0.027 R⊕) 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%.
Vanderburg , A , Becker , J C , Buchhave , L A , Mortier , A , Lopez , E , Malavolta , L , Haywood , R D , Latham , D W , Charbonneau , D , López-Morales , M , Adams , F C , Bonomo , A S , Bouchy , F , Collier Cameron , A , Cosentino , R , Di Fabrizio , L , Dumusque , X , Fiorenzano , A , Harutyunyan , A , Johnson , J A , Lorenzi , V , Lovis , C , Mayor , M , Micela , G , Molinari , E , Pedani , M , Pepe , F , Piotto , G , Phillips , D , Rice , K , Sasselov , D , Ségransan , D , Sozzetti , A , Udry , S & Watson , C 2017 , ' Precise masses in the WASP-47 system ' Astronomical Journal , vol 154 , no. 6 , 237 . DOI: 10.3847/1538-3881/aa918b
© 2017 The American Astronomical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.3847/1538-3881/aa918b
Funding: European Union Seventh Framework Programme (FP7/2007-2013) under Grant Agreement n.313014 (ETAEARTH). Parts of this work have been supported by NASA under grants No. NNX15AC90G and NNX17AB59G issued through the Exoplanets Research Program. This publication was made possible through the support of a grant from the John Templeton Foundation.
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