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

Balmer, William O.; Pueyo, Laurent; Stolker, Tomas; Reggiani, Henrique; Maire, A. -L.; Lacour, S.; Molliere, P.; Nowak, M.; Sing, D.; Pourre, 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.; Clenet, Y.; du Foresto, V. Coude; 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.; Houlle, M.; Hubert, Z.; Jocou, L.; Keppler, M.; Kervella, P.; Kreidberg, L.; Lagrange, A. -M.; Lapeyrere, V.; Le Bouquin, J. -B; Lena, 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.; ExoGRAVITY Collaboration; GRAVITY Collaboration
2023
ASTROPHYSICAL JOURNAL
DOI
10.3847/1538-4357/acf761
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 similar to 100 mu 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 M B = 69.5 +/- 0.5 M Jup assuming a strong prior on the host star mass M A = 0.97 +/- 0.01 M circle dot 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 +/- 2 sigma 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.