Letter to the Editor
First direct detection of an exoplanet by optical interferometry
LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
e-mail: email@example.com, firstname.lastname@example.org
2 Max Planck Institute for extraterrestrial Physics, Giessenbachstraße 1, 85748 Garching, Germany
3 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
4 1st Institute of Physics, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
5 Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
6 Universidade de Lisboa – Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal
7 Faculdade de Engenharia, Universidade do Porto, rua Dr. Roberto Frias, 4200-465 Porto, Portugal
8 European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
9 European Southern Observatory, Casilla 19001, Santiago 19, Chile
10 Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
11 Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
12 Sterrewacht Leiden, Leiden University, Postbus 9513, 2300 RA Leiden, The Netherlands
13 Departments of Physics and Astronomy, Le Conte Hall, University of California, Berkeley, CA 94720, USA
14 CENTRA – Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal
15 Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
16 Department of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
17 European Space Agency, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
18 Space Telescope Science Institute, Baltimore, MD 21218, USA
19 STAR Institute, Université de Liège, Allée du Six Août 19c, 4000 Liège, Belgium
20 Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
21 Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 70264, Ciudad de México 04510, Mexico
22 School of Physics, Astrophysics Group, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
Accepted: 28 February 2019
Aims. To date, infrared interferometry at best achieved contrast ratios of a few times 10−4 on bright targets. GRAVITY, with its dual-field mode, is now capable of high contrast observations, enabling the direct observation of exoplanets. We demonstrate the technique on HR 8799, a young planetary system composed of four known giant exoplanets.
Methods. We used the GRAVITY fringe tracker to lock the fringes on the central star, and integrated off-axis on the HR 8799 e planet situated at 390 mas from the star. Data reduction included post-processing to remove the flux leaking from the central star and to extract the coherent flux of the planet. The inferred K band spectrum of the planet has a spectral resolution of 500. We also derive the astrometric position of the planet relative to the star with a precision on the order of 100 μas.
Results. The GRAVITY astrometric measurement disfavors perfectly coplanar stable orbital solutions. A small adjustment of a few degrees to the orbital inclination of HR 8799 e can resolve the tension, implying that the orbits are close to, but not strictly coplanar. The spectrum, with a signal-to-noise ratio of ≈5 per spectral channel, is compatible with a late-type L brown dwarf. Using Exo-REM synthetic spectra, we derive a temperature of 1150 ± 50 K and a surface gravity of 104.3 ± 0.3 cm s2. This corresponds to a radius of 1.17−0.11+0.13 RJup and a mass of 10−4+7 MJup, which is an independent confirmation of mass estimates from evolutionary models. Our results demonstrate the power of interferometry for the direct detection and spectroscopic study of exoplanets at close angular separations from their stars.
Key words: stars: individual: HR 8799 / planets and satellites: atmospheres / planet-star interactions / techniques: interferometric
The reduced spectrum is available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/623/L11.
Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, ID 60.A-9102(G).
© S. Lacour et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.