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The Gemini Planet Imager Exoplanet Survey: Dynamical Mass of the Exoplanet β Pictoris b from Combined Direct Imaging and Astrometry

Nielsen, Eric L. and Wang, Jason J. (2020) The Gemini Planet Imager Exoplanet Survey: Dynamical Mass of the Exoplanet β Pictoris b from Combined Direct Imaging and Astrometry. Astronomical Journal, 159 (2). Art. No. 71. ISSN 1538-3881. doi:10.3847/1538-3881/ab5b92.

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We present new observations of the planet β Pictoris b from 2018 with the Gemini Planet Imager (GPI), the first GPI observations following conjunction. Based on these new measurements, we perform a joint orbit fit to the available relative astrometry from ground-based imaging, the Hipparcos Intermediate Astrometric Data (IAD), and the Gaia DR2 position, and demonstrate how to incorporate the IAD into direct imaging orbit fits. We find a mass consistent with predictions of hot-start evolutionary models and previous works following similar methods, though with larger uncertainties: 12.8^(+5.3)_(−3.2) M_(Jup). Our eccentricity determination of 0.12^(+0.04)_(-0.03) disfavors circular orbits. We consider orbit fits to several different imaging data sets, and find generally similar posteriors on the mass for each combination of imaging data. Our analysis underscores the importance of performing joint fits to the absolute and relative astrometry simultaneously, given the strong covariance between orbital elements. Time of conjunction is well-constrained within 2.8 days of 2017 September 13, with the star behind the planet's Hill sphere between 2017 April 11 and 2018 February 16 (±18 days). Following the recent radial velocity detection of a second planet in the system, β Pic c, we perform additional two-planet fits combining relative astrometry, absolute astrometry, and stellar radial velocities. These joint fits find a significantly smaller mass (8.0 ± 2.6 M_(Jup)) for the imaged planet β Pic b, in a somewhat more circular orbit. We expect future ground-based observations to further constrain the visual orbit and mass of the planet in advance of the release of Gaia DR4.

Item Type:Article
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URLURL TypeDescription Paper
Nielsen, Eric L.0000-0001-6975-9056
Wang, Jason J.0000-0003-0774-6502
Alternate Title:The Gemini Planet Imager Exoplanet Survey: Dynamical Mass of the Exoplanet beta Pictoris b from Combined Direct Imaging and Astrometry
Additional Information:© 2020 The American Astronomical Society. Received 2019 April 12; revised 2019 November 20; accepted 2019 November 23; published 2020 January 28. This work is based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), and Ministério da Ciência, Tecnologia e Inovação (Brazil). This research has made use of the SIMBAD and VizieR databases, operated at CDS, Strasbourg, France. This work has made use of data from the European Space Agency (ESA) mission Gaia (, processed by the Gaia Data Processing and Analysis Consortium (DPAC, Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562. J.R. and R.D. acknowledge support from the Fonds de Recherche du Québec. J.R.M.'s work was performed in part under contract with the California Institute of Technology (Caltech)/Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. Support for M.M.B.'s work was provided by NASA through Hubble Fellowship grant #51378.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. Supported by NSF grants AST-1411868 (E.L.N., K.B.F., B.M., J.P., and J.H.), AST-141378 (G.D.), and AST-1518332 (R.D.R., J.J.W., T.M.E., J.R.G., P.G.K.). Supported by NASA grants NNX14AJ80G (E.L.N., B.M., F.M., and M.P.), NNX15AC89G and NNX15AD95G (B.M., T.M.E., R.J.D.R., G.D., J.R.G., P.G.K.), NN15AB52l (D.S.), NSSC17K0535 (E.L.N., R.D.R., B.M., J.B.R.). J.J.W. is supported by the Heising-Simons Foundation 51 Pegasi b postdoctoral fellowship. Portions of this work were performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This work benefited from NASA's Nexus for Exoplanet System Science (NExSS) research coordination network, sponsored by NASA's Science Mission Directorate. Facility: Gemini:South (GPI) - . Software: Astropy (Astropy Collaboration et al. 2013), emcee (Foreman-Mackey et al. 2013), GPI DRP (Perrin et al. 2016), IDL Astronomy Library (Landsman 1993), pyKLIP (Wang et al. 2015).
Funding AgencyGrant Number
Gaia Multilateral AgreementUNSPECIFIED
Department of Energy (DOE)DE-AC02-05CH11231
Fonds de Recherche du QuébecUNSPECIFIED
NASA Hubble Fellowship51378.01-A
Heising-Simons Foundation51 Pegasi b Fellowship
Department of Energy (DOE)DE-AC52-07NA27344
Subject Keywords:Astrometry; Direct imaging; Exoplanets; Coronographic imaging; Orbit determination
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Astrometry (80); Direct imaging (387); Exoplanets (498); Coronographic imaging (313); Orbit determination (1175)
Record Number:CaltechAUTHORS:20200128-131432254
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Official Citation:Eric L. Nielsen et al 2020 AJ 159 71
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100965
Deposited By: Tony Diaz
Deposited On:28 Jan 2020 23:31
Last Modified:16 Nov 2021 17:58

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