An Updated Visual Orbit of the Directly Imaged Exoplanet 51 Eridani b and Prospects for a Dynamical Mass Measurement with Gaia

Creators: De Rosa, Robert J.; Wang, Jason J.

Abstract

We present a revision to the visual orbit of the young, directly imaged exoplanet 51 Eridani b using four years of observations with the Gemini Planet Imager. The relative astrometry is consistent with an eccentric (e = 0.53^(+0.09)_(−0.13)) orbit at an intermediate inclination (i = 136^(+10)_(−11)°), although circular orbits cannot be excluded due to the complex shape of the multidimensional posterior distribution. We find a semimajor axis of 11.1^(+4.2)_(−1.3) au and a period of 28.1^(+17.2)_(−4.9) yr, assuming a mass of 1.75 M⊙ for the host star. We find consistent values with a recent analysis of VLT/SPHERE data covering a similar baseline. We investigate the potential of using the absolute astrometry of the host star to obtain a dynamical mass constraint for the planet. The astrometric acceleration of 51 Eri derived from a comparison of the Hipparcos and Gaia catalogs was found to be inconsistent at the 2σ–3σ level with the predicted reflex motion induced by the orbiting planet. Potential sources of this inconsistency include a combination of random and systematic errors between the two astrometric catalogs and the signature of an additional companion within the system interior to current detection limits. We also explored the potential of using Gaia astrometry alone for a dynamical mass measurement of the planet by simulating Gaia measurements of the motion of the photocenter of the system over the course of the extended 8 yr mission. We find that such a measurement is only possible (>98% probability) given the most optimistic predictions for the Gaia scan astrometric uncertainties for bright stars and a high mass for the planet (≳3.6 M_(Jup)).

Additional Information

© 2019 The American Astronomical Society. Received 2019 April 11; revised 2019 October 10; accepted 2019 October 12; published 2019 December 10. We are grateful to the referee who helped to improve the quality of this work. We thank Trent Dupuy for useful discussions relating to this work. Supported by NSF grants AST-1411868 (R.D.R., 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., and P.G.K.). Supported by NASA grants NNX14AJ80G (R.D.R., E.L.N., B.M., F.M., and M.P.), NSSC17K0535 (R.D.R, E.L.N., B.M., and J.B.R.), and NNX15AC89G and NNX15AD95G (R.D.R., B.M., J.E.W., T.M.E., G.D., J.R.G., and P.G.K.). This work benefited from NASA's Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA's Science Mission Directorate. J.R. is supported by the French National Research Agency in the framework of the Investissements d'Avenir program (ANR-15-IDEX-02) through the funding of the "Origin of Life" project of the University Grenoble-Alpes. 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. V.P.B. acknowledges government sponsorship. Portions of this work were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. J.J.W. is supported by the Heising-Simons Foundation 51 Pegasi b postdoctoral fellowship. 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), National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), Ministério da Ciência, Tecnologia e Inovação (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). 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 No. ACI-1548562. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research has made use of the SIMBAD database and the VizieR catalog access tool, both operated at the CDS, Strasbourg, France. This research has made use of the Washington Double Star Catalog maintained at the U.S. Naval Observatory. Facility: Gemini:South (GPI). - Software: Astropy (The Astropy Collaboration et al. 2013), Matplotlib (Hunter 2007), pyKLIP (Wang et al. 2015).

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