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Sibley School of Mechanical and Aerospace Engineering

New article: Dynamical Constraints on the HR 8799 Planets with GPI

Article: Wang, JJ; Graham, JR; Dawson, R; Fabrycky, D; De Rosa, RJ; Pueyo, L; Konopacky, Q; Macintosh, B; Marois, C; Chiang, E; Ammons, SM; Arriaga, P; Bailey, VP; Barman, T; Bulger, J; Chilcote, J; Cotten, T; Doyon, R; Duchene, G; Esposito, TM; Fitzgerald, MP; Follette, KB; Gerard, BL; Goodsell, SJ; Greenbaum, AZ; Hibon, P; Hung, LW; Ingraham, P; Kalas, P; Larkin, JE; Maire, J; Marchis, F; Marley, MS; Metchev, S; Millar-Blanchaer, MA; Nielsen, L; Oppenheimer, R; Palmer, D; Patience, J; Perrin, M; Poyneer, L; Rajan, A; Rameau, J; Rantakyro, FT; Ruffio, JB; Savransky, D; Schneider, AC; Sivaramakrishnan, A; Song, I; Soummer, R; Thomas, S; Wallace, JK; Ward-Duong, K; Wiktorowicz, S; Wolfe, S; “Dynamical Constraints on the HR 8799 Planets with GPI”, Astronomical Journal, 156 (5)


Abstract:  The HR 8799 system uniquely harbors four young super-Jupiters whose orbits can provide insights into the system’s dynamical history and constrain the masses of the planets themselves. Using the Gemini Planet Imager, we obtained down to one milliarcsecond precision on the astrometry of these planets. We assessed four-planet orbit models with different levels of constraints and found that assuming the planets are near 1:2:4:8 period commensurabilities, or are coplanar, does not worsen the fit. We added the prior that the planets must have been stable for the age of the system (40 Myr) by running orbit configurations from our posteriors through N-body simulations and varying the masses of the planets. We found that only assuming the planets are both coplanar and near 1:2:4:8 period commensurabilities produces dynamically stable orbits in large quantities. Our posterior of stable coplanar orbits tightly constrains the planets’ orbits, and we discuss implications for the outermost planet b shaping the debris disk. A four-planet resonance lock is not necessary for stability up to now. However, planet pairs d and e, and c and d, are each likely locked in two-body resonances for stability if their component masses are above 6 M-Jup and 7 M-Jup, respectively. Combining the dynamical and luminosity constraints on the masses using hot-start evolutionary models and a system age of 42 +/- 5 Myr, we found the mass of planet b to be 5.8 +/- 0.5 M-Jup, and the masses of planets c, d, and e to be 7.2(-0.7)(+0.6) M-Jup each.

Funding Acknowledgement:  NSF [AST-1518332]; NASA [NNX15AC89G, NNX15AD95G, XRP 80NSSC18K0355]; NASA’s Science Mission Directorate; Pennsylvania State University; Eberly College of Science; Pennsylvania Space Grant Consortium; U.S. Department of Energy by Lawrence Livermore National Laboratory [DE-AC52-07NA27344]; Gemini Observatory

Funding Text:  Simulations in this paper made use of the REBOUND code, which can be downloaded freely at We thank Dan Tamayo for offering REBOUND tutorials and help with setting up the simulations. We also thank Eve Lee for helpful discussions on dynamics. J.J.W., J.R.G., P.K., and R.J.D. R. were supported in part by NSF AST-1518332, NASA NNX15AC89G, and NNX15AD95G. This work benefited from NASA’s Nexus for Exoplanet System Science (NExSS) research coordination network sponsored by NASA’s Science Mission Directorate. R.I.D. gratefully acknowledges support from NASA XRP 80NSSC18K0355. The Center for Exoplanets and Habitable Worlds is supported by the Pennsylvania State University, the Eberly College of Science, and the Pennsylvania Space Grant Consortium. 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.The GPI project has been supported by G  emini 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), the Australian Research Council (Australia), Ministerio da Ciencia, Tecnologia e Inovacao (Brazil), and Ministerio de Ciencia, Tecnologia e Innovacion Productiva (Argentina). This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France.

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