Letter to the Editor

Direct confirmation of the radial-velocity planet β Pictoris c

¹ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
e-mail: mcn35@cam.ac.uk
² Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
³ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 Place Jules Janssen, 92195 Meudon, France
⁴ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
⁵ Max Planck Institute for Extraterrestrial Physics, Giessenbachstraße 1, 85748 Garching, Germany
⁶ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁷ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁸ European Southern Observatory, Casilla, 19001 Santiago 19, Chile
⁹ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹⁰ Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
¹¹ Space Telescope Science Institute, Baltimore, MD 21218, USA
¹² Astronomy Department, University of Michigan, Ann Arbor, MI 48109, USA
¹³ School of Physics and Astronomy, Monash University, Clayton, Melbourne, VIC 3800, Australia
¹⁴ Center for Astrophysics and Planetary Science, Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
¹⁵ Institute of Physics, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
¹⁶ Universidade de Lisboa – Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal
¹⁷ CENTRA – Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal
¹⁸ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁹ School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
²⁰ Pasadena City College, Pasadena, CA 91106, USA
²¹ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
²² STAR Institute/Université de Liège, Liège, Belgium
²³ Center for Astrophysics | Harvard & Smithsonian, Cambridge, MA 02138, USA
²⁴ Pixyl, 5 Av. du Grand Sablon, 38700 La Tronche, France
²⁵ Research School of Astronomy & Astrophysics, Australian National University, Canberra, ACT 2611, Australia
²⁶ University of Exeter, Physics Building, Stocker Road, Exeter EX4 4QL, UK
²⁷ Institute for Particle Physics and Astrophysics, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
²⁸ Universidade do Porto, Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
²⁹ Five College Astronomy Department, Amherst College, Amherst, MA 01002, USA

Received: 27 July 2020
Accepted: 26 August 2020

Abstract

Context. Methods used to detect giant exoplanets can be broadly divided into two categories: indirect and direct. Indirect methods are more sensitive to planets with a small orbital period, whereas direct detection is more sensitive to planets orbiting at a large distance from their host star. This dichotomy makes it difficult to combine the two techniques on a single target at once.

Aims. Simultaneous measurements made by direct and indirect techniques offer the possibility of determining the mass and luminosity of planets and a method of testing formation models. Here, we aim to show how long-baseline interferometric observations guided by radial-velocity can be used in such a way.

Methods. We observed the recently-discovered giant planet β Pictoris c with GRAVITY, mounted on the Very Large Telescope Interferometer.

Results. This study constitutes the first direct confirmation of a planet discovered through radial velocity. We find that the planet has a temperature of T = 1250 ± 50 K and a dynamical mass of M = 8.2 ± 0.8 M_Jup. At 18.5 ± 2.5 Myr, this puts β Pic c close to a ‘hot start’ track, which is usually associated with formation via disk instability. Conversely, the planet orbits at a distance of 2.7 au, which is too close for disk instability to occur. The low apparent magnitude (M_K = 14.3 ± 0.1) favours a core accretion scenario.

Conclusions. We suggest that this apparent contradiction is a sign of hot core accretion, for example, due to the mass of the planetary core or the existence of a high-temperature accretion shock during formation.