First determination of the orbit of a binary L-dwarf
Hervé Bouy (Max-Planck-Institut für extraterrestrische Physik)
Wolfgang Brandner, Eduardo L. Martín, Jerôme Bouvier, Gaspard Duchene, Rainer Koehler
With spectral properties intermediate between those of giant planets and
late-type stars, ultra-cool and brown dwarfs have opened a new chapter in the
study of atmospheric physics and chemistry. One of the ultimate goals of a
theory of very low mass and sub-stellar objects is an accurate determination of
the mass of an object based on spectroscopic characteristics and luminosity. The
degeneracy in the mass-luminosity (age-temperature) relation for ultra-cool
dwarfs makes it difficult to pin down their physical properties. Luminosities
and effective temperatures of ultra-cool dwarfs are a function of
both age and mass so that an older, slightly more massive ultra-cool dwarf can
exhibit the same effective temperature as a younger, less massive
one. Therefore, dynamical masses, which are model-independent, are highly
required in order to calibrate the mass-luminosity relation.
We will present the results of astrometric, photometric and spectroscopic
observations leading to the determination of the orbit and dynamical masses of
the binary L dwarf 2MASSW J0746425+2000321. High angular resolution observations
spread over almost 4 years and obtained with the Hubble Space Telescope, the ESO
Very Large Telescope, and at the W. M. Keck Observatory
allow us to cover ≈ 60 % of the orbit, and, for the first time, to
derive a precise estimate of the total and individual masses of such a late-type
object.
http://www.mpe.mpg.de/~hbouy/