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New Insights on Planet Formation in WASP-47 from a Simultaneous Analysis of Radial Velocities and Transit Timing Variations

Weiss, Lauren M. and Deck, Katherine M. and Sinukoff, Evan and Petigura, Erik A. and Agol, Eric and Lee, Eve J. and Becker, Juliette C. and Howard, Andrew W. and Isaacson, Howard and Crossfield, Ian J. M. and Fulton, Benjamin J. and Hirsch, Lea and Benneke, Björn (2017) New Insights on Planet Formation in WASP-47 from a Simultaneous Analysis of Radial Velocities and Transit Timing Variations. Astronomical Journal, 153 (6). Art. No. 265. ISSN 0004-6256. https://resolver.caltech.edu/CaltechAUTHORS:20170619-140317982

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Abstract

Measuring precise planet masses, densities, and orbital dynamics in individual planetary systems is an important pathway toward understanding planet formation. The WASP-47 system has an unusual architecture that motivates a complex formation theory. The system includes a hot Jupiter ("b") neighbored by interior ("e") and exterior ("d") sub-Neptunes, and a long-period eccentric giant planet ("c"). We simultaneously modeled transit times from the Kepler K2 mission and 118 radial velocities to determine the precise masses, densities, and Keplerian orbital elements of the WASP-47 planets. Combining RVs and TTVs provides a better estimate of the mass of planet d (13.6 ± 2.0,M_⊕) than that obtained with only RVs (12.75 ± 2.70,M_⊕) or TTVs (16.1 3.8, M_⊕). Planets e and d have high densities for their size, consistent with a history of photoevaporation and/or formation in a volatile-poor environment. Through our RV and TTV analysis, we find that the planetary orbits have eccentricities similar to the solar system planets. The WASP-47 system has three similarities to our own solar system: (1) the planetary orbits are nearly circular and coplanar, (2) the planets are not trapped in mean motion resonances, and (3) the planets have diverse compositions. None of the current single-process exoplanet formation theories adequately reproduce these three characteristics of the WASP-47 system (or our solar system). We propose that WASP-47, like the solar system, formed in two stages: first, the giant planets formed in a gas-rich disk and migrated to their present locations, and second, the high-density sub-Neptunes formed in situ in a gas-poor environment.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-3881/aa6c29DOIArticle
http://iopscience.iop.org/article/10.3847/1538-3881/aa6c29/metaPublisherArticle
https://arxiv.org/abs/1612.04856arXivDiscussion Paper
ORCID:
AuthorORCID
Weiss, Lauren M.0000-0002-3725-3058
Sinukoff, Evan0000-0002-5658-0601
Petigura, Erik A.0000-0003-0967-2893
Agol, Eric0000-0002-0802-9145
Lee, Eve J.0000-0002-1228-9820
Becker, Juliette C.0000-0002-7733-4522
Howard, Andrew W.0000-0001-8638-0320
Isaacson, Howard0000-0002-0531-1073
Crossfield, Ian J. M.0000-0002-1835-1891
Fulton, Benjamin J.0000-0003-3504-5316
Hirsch, Lea0000-0001-8058-7443
Benneke, Björn0000-0001-5578-1498
Alternate Title:Mass and Eccentricity Constraints in the WASP-47 Planetary System from a Simultaneous Analysis of Radial Velocities and Transit Timing Variations
Additional Information:© 2017 American Astronomical Society. Received 2016 December 14. Accepted 2017 March 23. Published 2017 May 25. L.M.W. acknowledges the Trottier Family Foundation for their support. K.D. acknowledges the support of the JCPA fellowship at Caltech. E.S. is supported by a post-graduate scholarship from the Natural Sciences and Engineering Research Council of Canada. E.A. acknowledges support from NASA grants NNX13AF20G, NNX13AF62G, and the NASA Astrobiology Institutes Virtual Planetary Laboratory, supported by NASA under cooperative agreement NNH05ZDA001C. A.W.H. acknowledges support from a NASA Astrophysics Data Analysis Program grant, support from the K2 Guest Observer Program, and a NASA Key Strategic Mission Support Project. We thank Simon Walker for his help and generosity in using ttvfast-python. The authors thank Geoff Marcy, Eva Culakova, Daniel Fabrycky, Jack Lissauer, Jason Rowe, the Kepler-TTV working group, and the KITP Planet Formation and Dynamics workshop for useful discussions. We thank NASA and the Kepler team for the outstanding photometry that contributed to this paper. The authors wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain of Maunakea we are privileged to be guests. Without their generous hospitality, the Keck observations analyzed herein would not have been possible. Facilities: Keck:I (HIRES), Kepler.
Funders:
Funding AgencyGrant Number
Trottier Family FoundationUNSPECIFIED
Joint Center for Planetary Astronomy (JCPA)UNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
NASANNX13AF20G
NASANNX13AF20G
NASANNH05ZDA001C
Subject Keywords:planets and satellites: composition; planets and satellites: formation; planets and satellites: general; planets and satellites: individual (WASP-47 b, WASP-47 c, WASP-47 d, WASP-47 e)
Issue or Number:6
Record Number:CaltechAUTHORS:20170619-140317982
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170619-140317982
Official Citation:Lauren M. Weiss et al 2017 AJ 153 265
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78335
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:19 Jun 2017 22:22
Last Modified:11 Oct 2019 23:19

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