High contrast at short separation with VLTI/GRAVITY: Bringing Gaia companions to light

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
e-mail: nicolas.pourre@univ-grenoble-alpes.fr
² European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
³ LESIA, Observatoire de Paris, PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Janssen, 92195 Meudon, France
⁴ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁵ Universidade de Lisboa – Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal
⁶ CENTRA – Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal
⁷ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁸ Department of Physics & Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
⁹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁰ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA
¹¹ Max Planck Institute for extraterrestrial Physics, Giessenbachstraße 1, 85748 Garching, Germany
¹² Aix-Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹³ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Bd de l’Observatoire, CS 34229, 06304 Nice cedex 4, France
¹⁴ STAR Institute, Université de Liège, Allée du Six Août 19c, 4000 Liège, Belgium
¹⁵ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹⁶ Department of Astrophysical & Planetary Sciences, JILA, Duane Physics Bldg., 2000 Colorado Ave, University of Colorado, Boulder, CO 80309, USA
¹⁷ Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
¹⁸ Institute of Physics, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
¹⁹ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
²⁰ Universidade do Porto, Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
²¹ School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
²² School of Physics & Astronomy, University of Southampton, University Road, Southampton SO17 1BJ, UK
²³ Departments of Physics and Astronomy, Le Conte Hall, University of California, Berkeley, CA 94720, USA
²⁴ European Southern Observatory, Casilla 19001, Santiago 19, Chile
²⁵ Advanced Concepts Team, European Space Agency, TEC-SF, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
²⁶ University of Exeter, Physics Building, Stocker Road, Exeter EX4 4QL, UK
²⁷ Fakultät für Physik, Universität Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany
²⁸ Institüt für Astronomie und Astrophysik, Universität Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany
²⁹ Center for Space and Habitability, Universität Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
³⁰ Astronomy Department, University of Michigan, Ann Arbor, MI 48109 USA
³¹ Academia Sinica, Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, NTU/AS campus, No. 1, Section 4, Roosevelt Rd., Taipei 10617, Taiwan
³² European Space Agency (ESA), ESA Office, Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³³ Department of Earth & Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA
³⁴ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany
³⁵ Excellence Cluster ORIGINS, Boltzmannstraße 2, 85748 Garching bei München, Germany
³⁶ DOTA, ONERA, 13661 Salon cedex AIR, France
³⁷ KRP Mechatec GmbH, Boltzmannstraße 2, 85748 Garching bei München, Germany
³⁸ Universidad de Valparaíso, Instituto de Física y Astronomía (IFA), Avenida Gran Bretaña 1111, Casilla 5030, Valparaíso, Chile
³⁹ Núcleo Milenio de Formación Planetaria (NPF), Valparaíso, Chile
⁴⁰ Univ. Lyon 1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230, Saint-Genis-Laval, France

Received: 6 February 2024
Accepted: 24 March 2024

Abstract

Context. Since 2019, GRAVITY has provided direct observations of giant planets and brown dwarfs at separations of down to 95 mas from the host star. Some of these observations have provided the first direct confirmation of companions previously detected by indirect techniques (astrometry and radial velocities).

Aims. We want to improve the observing strategy and data reduction in order to lower the inner working angle of GRAVITY in dual-field on-axis mode. We also want to determine the current limitations of the instrument when observing faint companions with separations in the 30–150 mas range.

Methods. To improve the inner working angle, we propose a fiber off-pointing strategy during the observations to maximize the ratio of companion-light-to-star-light coupling in the science fiber. We also tested a lower-order model for speckles to decouple the companion light from the star light. We then evaluated the detection limits of GRAVITY using planet injection and retrieval in representative archival data. We compare our results to theoretical expectations.

Results. We validate our observing and data-reduction strategy with on-sky observations; first in the context of brown dwarf follow-up on the auxiliary telescopes with HD 984 B, and second with the first confirmation of a substellar candidate around the star Gaia DR3 2728129004119806464. With synthetic companion injection, we demonstrate that the instrument can detect companions down to a contrast of 8 × 10⁻⁴ (ΔΚ = 7.7 mag) at a separation of 35 mas, and a contrast of 3 × 10⁻⁵ (ΔΚ = 11 mag) at 100 mas from a bright primary (K < 6.5), for 30 min exposure time.

Conclusions. With its inner working angle and astrometric precision, GRAVITY has a unique reach in direct observation parameter space. This study demonstrates the promising synergies between GRAVITY and Gaia for the confirmation and characterization of substellar companions.