Follow-up observations of binary ultra-cool dwarfs

Abstract

Astrometric observations of resolved binaries provide estimates of orbital periods and will eventually lead to measurement of dynamical masses. Only a few very low mass star and brown dwarf masses have been measured to date, and the mass-luminosity relation still needs to be calibrated. We have monitored 14 very low mass multiple systems for several years to confirm their multiplicity and, for those with a short period, derive accurate orbital parameters and dynamical mass estimates. We have used high spatial resolution images obtained at the Paranal, Lick and HST observatories to obtain astrometric and photometric measurements of the multiple systems at several epochs. The targets have periods ranging from 5 to 200 years, and spectral types in the range M7.5 - T5.5. All of our 14 multiple systems are confirmed as common proper motion pairs. One system (2MASSW J0920122+351742) is not resolved in our new images, probably because the discovery images were taken near maximum elongation. Six systems have periods short enough to allow dynamical mass measurements within the next 15 to 20years. We estimate that only 8% of the ultracool dwarfs in the solar neighborhood are binaries with separations large enough to be resolved, and yet periods short enough to derive astrometric orbital fits over a reasonable time frame with current instrumentation. A survey that doubles the number of ultracool dwarfs observed with high angular resolution is called for to discover enough binaries for a first attempt to derive the mass-luminosity relationship for very low-mass stars and brown dwarfs.

13 pages, 6 Tables, 4 Figures, Accepted for A&A, reference pb corrected

References in corpus (28)

• The USNO-B Catalog
• Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs
• Sixty-seven Additional L Dwarfs Discovered by the Two Micron All Sky Survey (2MASS)
• New Neighbors from 2MASS: Activity and Kinematics at the Bottom of the Main Sequence
• Preliminary Parallaxes of 40 L and T Dwarfs from the U.S. Naval Observatory Infrared Astrometry Program
• The Spectra of T Dwarfs I: Near-Infrared Data and Spectral Classification
• Meeting the Cool New Neighbors V: A 2MASS-Selected Sample of Ultracool Dwarfs
• Binarity in Brown Dwarfs: T Dwarf Binaries Discovered with the Hubble Space Telescope WPFC2
• Detection of Nine M8.0-L0.5 Binaries: The Very Low Mass Binary Population and its Implications for Brown Dwarf and VLM Star Formation
• An Assessment of Dynamical Mass Constraints on Pre-Main Sequence Evolutionary Tracks
• Multiplicity of Nearby Free-floating Ultra-cool Dwarfs: a HST-WFPC2 search for companions
• Infrared Parallaxes for Methane T dwarfs
• A search for L dwarf binary systems
• Hubble Space Telescope Observations of Binary Very-Low-Mass Stars and Brown Dwarfs
• A Method for Determining the Physical Properties of the Coldest Known Brown Dwarfs
• Identifying Young Brown Dwarfs Using Gravity-Sensitive Spectral Features
• Four nearby L dwarfs
• Epsilon Indi Ba/Bb: the nearest binary brown dwarf
• Dynamical Masses of the Binary Brown Dwarf GJ 569Bab
• Discovery of Two Very Low-Mass Binaries: Final Results of an Adaptive Optics Survey of Nearby M6.0-M7.5 Stars
• First determination of the dynamical mass of a binary L dwarf
• An Adaptive Optics Survey of M8-M9 Stars: Discovery of 4 Very Low mass Binaries With at Least One System Containing a Brown Dwarf Companion
• Measuring Fundamental Parameters of Substellar Objects. II: Masses and Radii
• Multiplicity at the Stellar/Substellar Boundary in Upper Scorpius
• A possible third component in the L dwarf binary system DENIS-P J020529.0-115925 discovered with the Hubble Space Telescope
• Spectroscopic estimate of surface gravity for a planetary member in the Sigma Ori cluster
• A young binary Brown Dwarf in the R-CrA star formation region
• Resolved Hubble Space spectroscopy of ultracool binary systems

Cited by in corpus (20)

• The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition
• BANYAN. VII. A New Population of Young Substellar Candidate Members of Nearby Moving Groups from the BASS Survey
• Individual Dynamical Masses of Ultracool Dwarfs
• High Precision Dynamical Masses of Very Low Mass Binaries
• Keck Laser Guide Star Adaptive Optics Monitoring of 2MASS J1534-2952AB: First Dynamical Mass Determination of a Binary T Dwarf
• Discovery of a Highly Unequal-Mass Binary T Dwarf with Keck Laser Guide Star Adaptive Optics: A Coevality Test of Substellar Theoretical Models and Effective Temperatures
• On the Distribution of Orbital Eccentricities for Very Low-Mass Binaries
• Simultaneous Multiwavelength Observations of Magnetic Activity in Ultracool Dwarfs. IV. The Active, Young Binary NLTT 33370 AB (=2MASS J13142039+1320011)
• On the kinematic age of brown dwarfs: Radial velocities and space motions of 43 nearby L dwarfs
• New Brown Dwarf Companions to Young Stars in Scorpius-Centaurus
• Identification of a Wide, Low-Mass Multiple System Containing the Brown Dwarf 2MASS J0850359+105716
• Hubble Space Telescope Imaging and Spectral Analysis of Two Brown Dwarf Binaries at the L Dwarf/T Dwarf Transition
• Characterization of the Benchmark Binary NLTT 33370
• Binarity at the L/T brown dwarf transition
• The Future of Ultracool Dwarf Science with JWST
• Imaging survey of subsystems in secondary components to nearby southern dwarfs
• WISE J061213.85-303612.5: a new T-dwarf binary candidate
• Characterisation of close visual binaries from the AstraLux Large M Dwarf Survey
• Characterising Young Visual M-dwarf Binaries with Near-Infrared Integral Field Spectra
• Astrometric planet search around southern ultracool dwarfs IV. Relative motion of the FORS2/VLT CCD chips