VLTI/GRAVITY Observations and Characterization of the Brown Dwarf Companion HD 72946 B

October 2023 • 2023ApJ...956...99B

Authors • Balmer, William O. • Pueyo, Laurent • Stolker, Tomas • Reggiani, Henrique • Maire, A.-L. • Lacour, S. • Mollière, P. • Nowak, M. • Sing, D. • Pourré, N. • Blunt, S. • Wang, J. J. • Rickman, E. • Kammerer, J. • Henning, Th. • Ward-Duong, K. • Abuter, R. • Amorim, A. • Asensio-Torres, R. • Benisty, M. • Berger, J.-P. • Beust, H. • Boccaletti, A. • Bohn, A. • Bonnefoy, M. • Bonnet, H. • Bourdarot, G. • Brandner, W. • Cantalloube, F. • Caselli, P. • Charnay, B. • Chauvin, G. • Chavez, A. • Choquet, E. • Christiaens, V. • Clénet, Y. • Coudé Du Foresto, V. • Cridland, A. • Dembet, R. • Dexter, J. • Drescher, A. • Duvert, G. • Eckart, A. • Eisenhauer, F. • Gao, F. • Garcia, P. • Garcia Lopez, R. • Gendron, E. • Genzel, R. • Gillessen, S. • Girard, J. H. • Haubois, X. • Heißel, G. • Hinkley, S. • Hippler, S. • Horrobin, M. • Houllé, M. • Hubert, Z. • Jocou, L. • Keppler, M. • Kervella, P. • Kreidberg, L. • Lagrange, A.-M. • Lapeyrère, V. • Le Bouquin, J.-B. • Léna, P. • Lutz, D. • Monnier, J. D. • Mouillet, D. • Nasedkin, E. • Ott, T. • Otten, G. P. P. L. • Paladini, C. • Paumard, T. • Perraut, K. • Perrin, G. • Pfuhl, O. • Rameau, J. • Rodet, L. • Rousset, G. • Rustamkulov, Z. • Shangguan, J. • Shimizu, T. • Stadler, J. • Straub, O. • Straubmeier, C. • Sturm, E. • Tacconi, L. J. • van Dishoeck, E. F. • Vigan, A. • Vincent, F. • von Fellenberg, S. D. • Widmann, F. • Wieprecht, E. • Wiezorrek, E. • Winterhalder, T. • Woillez, J. • Yazici, S. • Young, A. • Gravity Collaboration

Abstract • Tension remains between the observed and modeled properties of substellar objects, but objects in binary orbits, with known dynamical masses, can provide a way forward. HD 72946 B is a recently imaged brown dwarf companion to a nearby, solar-type star. We achieve ~100 μas relative astrometry of HD 72946 B in the K band using VLTI/GRAVITY, unprecedented for a benchmark brown dwarf. We fit an ensemble of measurements of the orbit using orbitize! and derive a strong dynamical mass constraint M _B = 69.5 ± 0.5 M _Jup assuming a strong prior on the host star mass M _A = 0.97 ± 0.01 M _☉ from an updated stellar analysis. We fit the spectrum of the companion to a grid of self-consistent BT-Settl-CIFIST model atmospheres, and perform atmospheric retrievals using petitRADTRANS. A dynamical mass prior only marginally influences the sampled distribution of effective temperature, but has a large influence on the surface gravity and radius, as expected. The dynamical mass alone does not strongly influence retrieved pressure-temperature or cloud parameters within our current retrieval setup. Independently of the cloud prescription and prior assumptions, we find agreement within ±2σ between the C/O of the host (0.52 ± 0.05) and brown dwarf (0.43-0.63), as expected from a molecular cloud collapse formation scenario, but our retrieved metallicities are implausibly high (0.6-0.8) in light of the excellent agreement of the data with the solar-abundance model grid. Future work on our retrieval framework will seek to resolve this tension. Additional study of low surface gravity objects is necessary to assess the influence of a dynamical mass prior on atmospheric analysis.

Links

• SIMBAD https://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2023ApJ...956...99B
• PDF https://iopscience.iop.org/article/10.3847/1538-4357/acf761/pdf
• PREPRINT http://arxiv.org/abs/2309.04403
• DATA http://archive.eso.org/bin/ads2eso?2023ApJ...956...99B
• DATA https://irsa.ipac.caltech.edu/bibdata/2023/B/2023ApJ...956...99B.html
• ELECTR https://doi.org/10.3847/1538-4357/acf761