An updated visual orbit of the directly-imaged Exoplanet 51 Eridani b and prospects for a dynamical mass measurement with Gaia

Robert J. de Rosa, Eric L. Nielsen, Jason J. Wang, S. Mark Ammons, Gaspard Duchêne, Bruce Macintosh, Meiji M. Nguyen, Julien Rameau, Vanessa P. Bailey, Travis Barman, Joanna Bulger, Jeffrey Chilcote, Tara Cotten, Rene Doyon, Thomas M. Esposito, Michael P. Fitzgerald, Katherine B. Follette, Benjamin L. Gerard, Stephen J. Goodsell, James R. GrahamAlexandra Z. Greenbaum, Pascale Hibon, Justin Hom, Li Wei Hung, Patrick Ingraham, Paul Kalas, Quinn Konopacky, James E. Larkin, Jérôme Maire, Franck Marchis, Mark S. Marley, Christian Marois, Stanimir Metchev, Maxwell A. Millar-Blanchaer, Rebecca Oppenheimer, David Palmer, Jennifer Patience, Marshall Perrin, Lisa Poyneer, Laurent Pueyo, Abhijith Rajan, Fredrik T. Rantakyrö, Bin Ren, Jean Baptiste Ruffio, Dmitry Savransky, Adam C. Schneider, Anand Sivaramakrishnan, Inseok Song, Remi Soummer, Melisa Tallis, Sandrine Thomas, J. Kent Wallace, Kimberly Ward-Duong, Sloane Wiktorowicz, Schuyler Wolff

Research output: Contribution to journalArticlepeer-review


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+00..0913) orbit at an intermediate inclination (i = 136+1011 deg), although circular orbits cannot be excluded due to the complex shape of the multidimensional posterior distribution. We find a semi-major axis of 11.1+41..23 au and a period of 28.1+174.9.2 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 investigated the potential of using 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 catalogues was found to be inconsistent at the 2–3σ 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 or 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 eight-year 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 MJup).

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Oct 22 2019


  • Astrometry
  • Planets and satellites: fundamental parameters
  • Stars: individual (51 Eridani)
  • Techniques: high angular resolution

ASJC Scopus subject areas

  • General

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