VLTI/GRAVITY Observations and Characterization of the Brown Dwarf Companion HD 72946 B
Creators: name: Balmer, W. O.
name: Pueyo, L.
name: Stolker, T.
name: Reggiani, H.
name: Lacour, S.
name: Maire, A. -L.
name: Mollière, P.
name: Nowak, M.
name: Sing, D.
name: Pourré, N.
name: Blunt, S.
name: Wang, J. J.
name: Rickman, E.
name: Henning, Th.
name: Ward-Duong, K.
name: Abuter, R.
name: Amorim, A.
name: Asensio-Torres, R.
name: Benisty, M.
name: Berger, J. -P.
name: Beust, H.
name: Boccaletti, A.
name: Bohn, A.
name: Bonnefoy, M.
name: Bonnet, H.
name: Bourdarot, G.
name: Brandner, W.
name: Cantalloube, F.
name: Caselli, P.
name: Charnay, B.
name: Chauvin, G.
name: Chavez, A.
name: Choquet, E.
name: Christiaens, V.
name: Clénet, Y.
name: Foresto, V. Coudé du
name: Cridland, A.
name: Dembet, R.
name: Drescher, A.
name: Duvert, G.
name: Eckart, A.
name: Eisenhauer, F.
name: Feuchtgruber, H.
name: Garcia, P.
name: Lopez, R. Garcia
name: Gardner, T.
name: Gendron, E.
name: Genzel, R.
name: Gillessen, S.
name: Girard, J. H.
name: Haubois, X.
name: Heißel, G.
name: Hinkley, S.
name: Hippler, S.
name: Horrobin, M.
name: Houllé, M.
name: Hubert, Z.
name: Jocou, L.
name: Kammerer, J.
name: Keppler, M.
name: Kervella, P.
name: Kreidberg, L.
name: Lagrange, A. -M.
name: Lapeyrère, V.
name: Bouquin, J. -B. Le
name: Léna, P.
name: Lutz, D.
name: Mang, F.
name: Marleau, G. -D.
name: Mérand, A.
name: Monnier, J. D.
name: Mordasini, C.
name: Mouillet, D.
name: Nasedkin, E.
name: Ott, T.
name: Otten, G. P. P. L.
name: Paladini, C.
name: Paumard, T.
name: Perraut, K.
name: Perrin, G.
name: Pfuhl, O.
name: Rameau, J.
name: Rodet, L.
name: Rustamkulov, Z.
name: Shangguan, J.
name: Shimizu, T.
name: Straubmeier, C.
name: Sturm, E.
name: Tacconi, L. J.
name: van Dishoeck, E. F.
name: Vigan, A.
name: Vincent, F.
name: Widmann, F.
name: Wieprecht, E.
name: Wiezorrek, E.
name: Winterhalder, T.
name: Woillez, J.
name: Yazici, S.
name: Young, A.
Publisher: name: arXiv
Year: 2023
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: 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 the nearby, solar type star. We achieve $\sim100~μ\mathrm{as}$ 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 $\mathrm{M_B}=69.5\pm0.5~\mathrm{M_{Jup}}$ assuming a strong prior on the host star mass $\mathrm{M_A}=0.97\pm0.01~\mathrm{M_\odot}$ 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 on 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. Independent of cloud prescription and prior assumptions, we find agreement within $\pm2\,σ$ between the C/O ratio of the host ($0.52\pm0.05)$ and brown dwarf ($0.43$ to $0.63$), as expected from a molecular cloud collapse formation scenario, but our retrieved metallicities are implausibly high ($0.6-0.8$) in light of an 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.
description: Accepted for publication in the Astrophysical Journal. 32 pages, 14 figures, 7 tables. v2&amp;3 correct errors in co-author's affiliations, figure rendering, and some grant acknowledgements