brown dwarfs; methods: data analysis; stars: individual: HD 72946; planets and satellites: dynamical evolution and stability; techniques: high angular resolution; techniques: image processing
Abstract :
[en] Context. HD 72946 is a bright and nearby solar-type star hosting a low- mass companion at long period (P ̃ 16 yr) detected with the radial velocity (RV) method. The companion has a minimum mass of 60.4 ± 2.2 M[SUB]J[/SUB] and might be a brown dwarf. Its expected semi-major axis of ̃243 mas makes it a suitable target for further characterization with high-contrast imaging, in particular to measure its inclination, mass, and spectrum and thus definitely establish its substellar nature. <BR /> Aims: We aim to further characterize the orbit, atmosphere, and physical nature of HD 72946B. <BR /> Methods: We present high-contrast imaging data in the near-infrared with the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE) instrument. We also use proper motion measurements of the star from HIPPARCOS and Gaia. <BR /> Results: The SPHERE data reveal a point source with a contrast of ̃9 mag at a projected separation of ̃235 mas. No other point sources are detected in the field of view. By jointly fitting the RV, imaging, and proper motion data, we constrain all the orbital parameters of HD 72946B and assess a dynamical mass of 72.4 ± 1.6 M[SUB]J[/SUB] and a semi-major axis of 6.456.45[SUP]+0.08[/SUP][SUB]-0.07[/SUB] au. Empirical comparison of its SPHERE spectrum to template dwarfs indicates a spectral type of L5.0 ± 1.5. The J-H3 color is close to the expectations of the DUSTY models and suggests a cloudy atmosphere. Comparison with atmospheric models of the spectrophotometry suggests an effective temperature of ̃1700 K. The bolometric luminosity (log(L/L[SUB]☉[/SUB]) = -4.11 ± 0.10 dex) and dynamical mass of HD 72946B are more compatible with evolutionary models for an age range of ̃0.9-3 Gyr. The formation mechanism of the companion is currently unclear as the object appears slightly away from the bulk of model predictions. HD 72946B is currently the closest benchmark brown dwarf companion to a solar-type star with imaging, RV, and proper motion measurements. <P />Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 0102.C-0781.
Research Center/Unit :
STAR - Space sciences, Technologies and Astrophysics Research - ULiège
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Maire, Anne-Lise ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > PSILab
Baudino, J.-L.; Department of Physics, University of Oxford, Oxford, UK
Messina, S.; INAF Catania Astrophysical Observatory, Via S. Sofia 78, 95123, Catania, Italy
Brandner, W.; Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany
Godoy, N.; Instituto de Física y Astronomía, Facultad de Ciencias, Univ. de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile ; Núcleo Milenio Formación Planetaria - NPF, Univ. de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
Cantalloube, F.; Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany
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Absil, Olivier ; Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > PSILab
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