The ExoGRAVITY survey: A <i>K</i> -band spectral library of giant exoplanet and brown dwarf companions

Context . Direct observations of exoplanet and brown dwarf companions with near-infrared interferometry, first enabled by the dualfield mode of VLTI/GRAVITY, provide unique measurements of the objects’ orbital motions and atmospheric compositions. Aims . Here we compile a homogeneous library of all exoplanet and brown dwarf K -band spectra observed by GRAVITY thus far. This ExoGRAVITY Spectral Library is made publicly available online. Methods . We re-reduced all the available GRAVITY dual-field high-contrast data in a uniform and highly automated way and, where companions were detected, extracted their ~2.0-2.4 μm K -band contrast spectra. We then derived stellar model atmospheres for all the employed flux references (either the host star or the swap calibrator), which we used to convert the companion contrast into companion flux spectra. Solely from the resulting GRAVITY K -band flux spectra, we extracted spectral types, spectral indices, and bulk physical properties for all the companions. Finally, and with the help of age constraints from the literature, we also derived isochronal masses for most of the companions using evolutionary models. Results . The resulting library contains R ~ 500 GRAVITY K -band spectra of 39 substellar companions from late M to late T spectral types, including the entire L-T transition. Throughout this transition, a shift from CO-dominated late M- and L-type dwarfs to CH 4 -dominated T-type dwarfs can be observed in the K -band. The GRAVITY spectra alone constrain the objects’ bolometric luminosity to typically within ±0.15 dex. The derived isochronal masses agree with dynamical masses from the literature where available, except for HD 4113 c for which we confirm its previously reported potential underluminosity. Conclusions . Medium-resolution spectroscopy of substellar companions with GRAVITY provides insight into the carbon chemistry and the cloudiness of these objects’ atmospheres. It also constrains these objects’ bolometric luminosities, which can yield measurements of their formation entropy if combined with dynamical masses, for instance from Gaia and GRAVITY astrometry.

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Journal
Astronomy and Astrophysics
Published
2025-11-04
DOI
https://doi.org/10.1051/0004-6361/202556860
Citations
1
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
1.15

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article

The ExoGRAVITY survey: A K -band spectral library of giant exoplanet and brown dwarf companions

É. Gendron, M. Bonnefoy, O. Straub, Gabriel-Dominique Marleau et al.
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Stellar, planetary, and galactic studies
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article

The ExoGRAVITY survey: A K -band spectral library of giant exoplanet and brown dwarf companions

É. Gendron, M. Bonnefoy, O. Straub, Gabriel-Dominique Marleau, C. Straubmeier, S. Lacour, V. Lapeyrère, C. Paladini, M. Houllé, S. Udry, Élodie Choquet, J. Hagelberg, S. Hippler, A. Drescher, William O. Balmer, A. Cridland, Jean-Philippe Berger, W. Ceva, S. Gillessen, F. Cantalloube, F. Vincent, D. Ségransan, A. Chomez, L. Kreidberg, L. Piscarreta, T. Paumard, Y. Clénet, T. Stolker, J. Stadler, C. Mordasini, Sarah Blunt, A. Eckart, A. Mérand, T. Forveille, S. Hinkley, G. Perrin, J. Wang, D. Lutz, A. Boccaletti, K. Perraut, Zafar Rustamkulov, Julien M. Woillez, M. Samland, L. Jocou, F. Mang, F. Widmann, Thomas Shimizu, W. Brandner, H. Beust, Valentin Christiaens, G. Duvert, Ş. Yazıcı, A. Amorim, N. Pourré, C. Fontanive, J. Kammerer, B. Charnay, E. Nasedkin, Anna Moore, S. Grant, F. Eisenhauer, P. Mollière, J.-B. Le Bouquin, David K. Sing, Thomas Henning, Claudia Toci, P. Kervella, R. Dembet, A.-M. Lagrange, R. Genzel, P. García, A. Vigan, M. Keppler, Thomas Ott, P. Caselli, T. O. Winterhalder, X. Haubois, R. Garcia Lopez, J. Dexter, Laurent Pueyo, E. Sturm, R. Abuter, G. Chauvin, A.-L. Maire, O. Pfuhl, V. Coudé du Foresto, R. Davies, Z. Hubert, J. Shangguan, A. Chavez, H. Bonnet, G. Bourdarot, D. Mouillet
article en
1 citations

Abstract

Context . Direct observations of exoplanet and brown dwarf companions with near-infrared interferometry, first enabled by the dualfield mode of VLTI/GRAVITY, provide unique measurements of the objects’ orbital motions and atmospheric compositions. Aims . Here we compile a homogeneous library of all exoplanet and brown dwarf K -band spectra observed by GRAVITY thus far. This ExoGRAVITY Spectral Library is made publicly available online. Methods . We re-reduced all the available GRAVITY dual-field high-contrast data in a uniform and highly automated way and, where companions were detected, extracted their ~2.0-2.4 μm K -band contrast spectra. We then derived stellar model atmospheres for all the employed flux references (either the host star or the swap calibrator), which we used to convert the companion contrast into companion flux spectra. Solely from the resulting GRAVITY K -band flux spectra, we extracted spectral types, spectral indices, and bulk physical properties for all the companions. Finally, and with the help of age constraints from the literature, we also derived isochronal masses for most of the companions using evolutionary models. Results . The resulting library contains R ~ 500 GRAVITY K -band spectra of 39 substellar companions from late M to late T spectral types, including the entire L-T transition. Throughout this transition, a shift from CO-dominated late M- and L-type dwarfs to CH 4 -dominated T-type dwarfs can be observed in the K -band. The GRAVITY spectra alone constrain the objects’ bolometric luminosity to typically within ±0.15 dex. The derived isochronal masses agree with dynamical masses from the literature where available, except for HD 4113 c for which we confirm its previously reported potential underluminosity. Conclusions . Medium-resolution spectroscopy of substellar companions with GRAVITY provides insight into the carbon chemistry and the cloudiness of these objects’ atmospheres. It also constrains these objects’ bolometric luminosities, which can yield measurements of their formation entropy if combined with dynamical masses, for instance from Gaia and GRAVITY astrometry.

Astronomy and AstrophysicsVol. 704
University College Dublin (IE), University of Geneva (CH), University of Bern (CH), Leiden University (NL), Centre National de la Recherche Scientifique (FR), Space Telescope Science Institute (US), Planetary Science Institute (US), Institute of Astronomy and Astrophysics, Academia Sinica (TW), Joint Institute for Laboratory Astrophysics (US), University of Lisbon (PT), Johns Hopkins University (US), University of Liège (BE), University of Cologne (DE), Universidade do Porto (PT), Trinity College Dublin (IE), Aix-Marseille Université (FR), University of Exeter (GB), Université Paris Sciences et Lettres (FR), University College Cork (IE), University of Michigan (US), Observatoire de Paris (FR), European Space Agency (FR), Sorbonne Université (FR), Institute of Astrophysics and Space Sciences (PT), Max Planck Institute for Extraterrestrial Physics (DE), Kavli Institute for Particle Astrophysics and Cosmology (US), Excellence Cluster Origins (DE), Max Planck Institute for Astrophysics (DE), Royal Observatory (GB), Max Planck Institute for Astronomy (DE), Laboratoire d’études spatiales et d’instrumentation en astrophysique (FR), Observatoire de la Côte d’Azur (FR), Astronomy and Space (AU), Max Planck Institute for Radio Astronomy (DE), Lunar and Planetary Institute (US), University of Duisburg-Essen (DE), Universidade Nova de Lisboa (PT), Université Grenoble Alpes (FR), University of Edinburgh (GB)
National Aeronautics and Space Administration, European Space Agency, European Commission, Agence Nationale de la Recherche, Nuclear Safety and Security Commission, Agencia Estatal de Investigación
Openalex Percentile: Top 15%
Stellar, planetary, and galactic studies
1.15
DOIOpen Access PDFOpenAlex
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