Astrometric orbits of spectral binary brown dwarfs - I. Massive T dwarf companions to 2M1059-21 and 2M0805+48

J. Sahlmann , A. J. Burgasser , D. C. Bardalez Gagliuffi , P. F. Lazorenko , D. Ségransan , M. R. Zapatero Osorio , C. H. Blake , C. R. Gelino , E. L. Martín , H. Bouy (1)

1 LAB - Laboratoire d'Astrophysique de Bordeaux [Pessac]

Near-infrared spectroscopic surveys have uncovered a population of short-period, blended-light spectral binaries composed of low-mass stars and brown dwarfs. These systems are amenable to orbit determination and individual mass measurements via astrometric monitoring. Here, we present first results of a multiyear campaign to obtain high-precision absolute astrometry for spectral binaries using the Gemini-South and Gemini-North GMOS imagers. We measure the complete astrometric orbits for two systems: 2M0805+48 and 2M1059-21. Our astrometric orbit of 2M0805+48 is consistent with its 2-yr radial velocity orbit determined previously and we find a mass of 66_-14⁺⁵ M_Jup for its T5.5 companion. For 2M1059-21, we find a 1.9-yr orbital period and a mass of 67_-5⁺⁴ M_Jup for its T3.5 companion. We demonstrate that sub-milliarcsecond absolute astrometry can be obtained with both GMOS imagers and that this is an efficient avenue for confirming and characterizing ultracool binary systems.

Keywords: binaries: close; brown dwarfs; astrometry; parallaxes; stars: low-mass

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]

J. Sahlmann, A. J. Burgasser, D. C. Bardalez Gagliuffi, P. F. Lazorenko, D. Ségransan, et al.. Astrometric orbits of spectral binary brown dwarfs - I. Massive T dwarf companions to 2M1059-21 and 2M0805+48. Monthly Notices of the Royal Astronomical Society, 2020, 495, pp.1136-1147. ⟨10.1093/mnras/staa1235⟩. ⟨insu-03678867⟩