The ExoGRAVITY survey: A K -band spectral library of giant exoplanet and brown dwarf companions
Year: 2025
Type: article
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.
Source: Astronomy and Astrophysics
Authors: J. Kammerer, T. O. Winterhalder, S. Lacour, T. Stolker, G.-D. Marleau, W. O. Balmer, A. F. Moore, L. Piscarreta, C. Toci, A. Mérand, M. Nowak, E. L. Rickman, L. Pueyo, N. Pourré, E. Nasedkin, J. J. Wang, G. Bourdarot, F. Eisenhauer, Th. Henning, R. Garcia Lopez, E. F. van Dishoeck, T. Forveille, J. D. Monnier, R. Abuter, A. Amorim, M. Benisty, J.-P. Berger, H. Beust, S. Blunt, A. Boccaletti, M. Bonnefoy, H. Bonnet, M. S. Bordoni, W. Brandner, F. Cantalloube, P. Caselli, W. Ceva, B. Charnay, G. Chauvin, A. Chavez, A. Chomez, E. Choquet, V. Christiaens, Y. Clénet, V. Coudé du Foresto, A. Cridland, R. Davies, R. Dembet, J. Dexter, A. Drescher, G. Duvert, A. Eckart, C. Fontanive, N. M. Förster Schreiber, P. Garcia, E. Gendron, R. Genzel, S. Gillessen, J. H. Girard, S. Grant, J. Hagelberg, X. Haubois, G. Heißel, S. Hinkley, S. Hippler, M. Houllé, Z. Hubert, L. Jocou, M. Keppler, P. Kervella, L. Kreidberg, N. T. Kurtovic, A.-M. Lagrange, V. Lapeyrère, J.-B. Le Bouquin, D. Lutz, A.-L. Maire, F. Mang, E. C. Matthews, P. Mollière, C. Mordasini, D. Mouillet, T. Ott, G. P. P. L. Otten, C. Paladini, T. Paumard, K. Perraut, G. Perrin, O. Pfuhl, D. C. Ribeiro, Z. Rustamkulov, D. Ségransan, J. Shangguan, T. Shimizu, M. Samland, D. Sing, J. Stadler, O. Straub, C. Straubmeier, E. Sturm, L. J. Tacconi, S. Udry, A. Vigan, F. Vincent, S. D. von Fellenberg, F. Widmann, J. Woillez, S. Yazici
Institutions: European Southern Observatory, European Southern Observatory, Centre National de la Recherche Scientifique, Université Paris Sciences et Lettres, Observatoire de Paris, Sorbonne Université, Laboratoire d’études spatiales et d’instrumentation en astrophysique, Leiden University, Leiden Observatory, University of Bern, Max Planck Institute for Astronomy, University of Duisburg-Essen, Space Telescope Science Institute, Johns Hopkins University, University College Cork, European Space Agency, Institut de Planétologie et d'Astrophysique de Grenoble, Université Grenoble Alpes, Trinity College Dublin, Northwestern University, Max Planck Institute for Extraterrestrial Physics, University College Dublin, University of Michigan, University of Lisbon, Instituto Superior Técnico, Centro de Astrofísica e Gravitação, University of Geneva, Université Côte d'Azur, Lagrange Laboratory, Observatoire de la Côte d’Azur, Aix-Marseille Université, University of Liège, Joint Institute for Laboratory Astrophysics, University of Cologne, Max Planck Institute for Radio Astronomy, Royal Observatory, University of Edinburgh, Universidade do Porto, University of California System, European Space Research and Technology Centre, University of Exeter, Center for Space and Habitability, Institute of Astronomy and Astrophysics, Academia Sinica, Academia Sinica, Peking University, Excellence Cluster Origins, Max Planck Institute for Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W4415885587