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

Abstract

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 multi-year 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-year radial velocity orbit determined previously and we find a mass of $66_{-14}^{+5}{M}_{\mathrm{Jup}}$ for its T5.5 companion. For 2M1059$-$21 we find a 1.9 year orbital period and a mass of $67_{-5}^{+4}{M}_{\mathrm{Jup}}$ 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 characterising ultracool binary systems.

14 pages, 13 figures, accepted for publication in MNRAS

References in corpus (22)

• The Gaia mission
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• The 0.8-14.5 micron Spectra of Mid-L to Mid-T Dwarfs: Diagnostics of Effective Temperature, Grain Sedimentation, Gas Transport, and Surface Gravity
• Young L Dwarfs Identified in the Field: A Preliminary Low-Gravity, Optical Spectral Sequence from L0 to L5
• A Low-Mass Planet with a Possible Sub-Stellar-Mass Host in Microlensing Event MOA-2007-BLG-192
• Chromospheric Activity, Rotation, and Rotational Braking in M and L Dwarfs
• Radio Observations of a Large Sample of Late-M, L, and T Dwarfs: The Distribution of Magentic Field Strengths
• A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
• Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
• The CARMENES search for exoplanets around M dwarfs: Different roads to radii and masses of the target stars
• Subtle Signatures of Multiplicity in Late-type Dwarf Spectra: The Unresolved M8.5 + T5 Binary 2MASS J03202839-0446358
• New Evidence for a Substellar Luminosity Problem: Dynamical Mass for the Brown Dwarf Binary Gl 417BC
• SDSS J080531.84+481233.0: An Unresolved L Dwarf/T Dwarf Binary
• WISE J072003.20-084651.2: An Old and Active M9.5 + T5 Spectral Binary 6 pc from the Sun
• Astrometric planet search around southern ultracool dwarfs I: First results, including parallaxes of 20 M8-L2 dwarfs
• A Spectroscopic Binary at the M/L Transition
• Trigonometric Parallaxes for Two Late-Type Subdwarfs: LSR1425+71 (sdM8.0) and the Binary LSR1610-00 (sd?M6pec)
• The Mass-Activity relationships in M and K dwarfs. I. Stellar parameters of our sample of M and K dwarfs
• The mass of planet GJ676A b from ground-based astrometry: A planetary system with two mature gas giants suitable for direct imaging
• Astrometric planet search around southern ultracool dwarfs III. Discovery of a brown dwarf in a 3-year orbit around DE0630-18
• Astrometric planet search around southern ultracool dwarfs II: Astrometric reduction methods and a deep astrometric catalogue
• An Age Constraint for the Very Low-Mass Stellar/Brown Dwarf Binary 2MASS J03202839-0446358AB

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