S. Lacour, Sorbonne Université
J. J. Wang, California Institute of Technology
L. Rodet, Cornell Center for Astrophysics and Planetary Science
M. Nowak, Institute of Astronomy
J. Shangguan, Max Planck Institute for Extraterrestrial Physics
H. Beust, Université Grenoble Alpes
A. M. Lagrange, Sorbonne Université
R. Abuter, European Southern Observatory
A. Amorim, Faculdade de Ciências, Universidade de Lisboa
R. Asensio-Torres, Max Planck Institute for Astronomy
M. Benisty, Université Grenoble Alpes
J. P. Berger, Université Grenoble Alpes
S. Blunt, California Institute of Technology
A. Boccaletti, Sorbonne Université
A. Bohn, Sterrewacht Leiden
M. L. Bolzer, Max Planck Institute for Extraterrestrial Physics
M. Bonnefoy, Université Grenoble Alpes
H. Bonnet, European Southern Observatory
G. Bourdarot, Max Planck Institute for Extraterrestrial Physics
W. Brandner, Max Planck Institute for Astronomy
F. Cantalloube, Laboratoire d'Astrophysique de Marseille
P. Caselli, Max Planck Institute for Extraterrestrial Physics
B. Charnay, Sorbonne Université
G. Chauvin, Université Grenoble Alpes
E. Choquet, Laboratoire d'Astrophysique de Marseille
V. Christiaens, Monash University
Y. Clénet, Sorbonne Université
V. Coudé Du Foresto, Sorbonne Université
A. Cridland, Sterrewacht Leiden
R. Dembet, European Southern Observatory
J. Dexter, University of Colorado Boulder
P. T. De Zeeuw, Max Planck Institute for Extraterrestrial Physics
K. Ward-Duong, Smith CollegeFollow
et al, Various Institutions

Document Type


Publication Date


Publication Title

Astronomy and Astrophysics


Aims. We aim to demonstrate that the presence and mass of an exoplanet can now be effectively derived from the astrometry of another exoplanet. Methods. We combined previous astrometry of β Pictoris b with a new set of observations from the GRAVITY interferometer. The orbital motion of β Pictoris b is fit using Markov chain Monte Carlo simulations in Jacobi coordinates. The inner planet, β Pictoris c, was also reobserved at a separation of 96 mas, confirming the previous orbital estimations. Results. From the astrometry of planet b only, we can (i) detect the presence of β Pictoris c and (ii) constrain its mass to 10.04-3.10+4.53 MJup. If one adds the astrometry of β Pictoris c, the mass is narrowed down to 9.15-1.06+1.08 MJup. The inclusion of radial velocity measurements does not affect the orbital parameters significantly, but it does slightly decrease the mass estimate to 8.89-0.75+0.75 MJup. With a semimajor axis of 2.68 ± 0.02 au, a period of 1221 ± 15 days, and an eccentricity of 0.32 ± 0.02, the orbital parameters of β Pictoris c are now constrained as precisely as those of β Pictoris b. The orbital configuration is compatible with a high-order mean-motion resonance (7:1). The impact of the resonance on the planets' dynamics would then be negligible with respect to the secular perturbations, which might have played an important role in the eccentricity excitation of the outer planet.


Astrometry, Instrumentation: high angular resolution, Instrumentation: interferometers, Planets and satellites: detection








© S. Lacour et al. 2021


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