Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21330303s&link_type=abstract
American Astronomical Society, AAS Meeting #213, #303.03; Bulletin of the American Astronomical Society, Vol. 41, p.272
Astronomy and Astrophysics
Astronomy
Scientific paper
With spectral properties intermediate between those of late-type stars and giant planets the observations of brown dwarfs play a crucial role. As brown dwarfs never stabilize on the hydrogen burning main sequence, there is no unambiguous mass-luminosity relation. This makes it hard to determine their physical properties and to test theories of formation processes. Spatially resolved BD binaries provide the unique opportunity to determine the dynamical masses of the binary components independently of theoretical models. Thus we started a high-resolution spectroscopic and photometric monitoring program with the VLT NGS and LGS AO systems, to observe binary BDs with relatively short orbital periods, covering the spectral range from early L, across the particularly interesting L/T transition to the T dwarfs. In addition, we carried out a spectral differential imaging program with HST/NICMOS, to search for planetary mass companions. As targets we chose 12 isolated L dwarfs in the solar neighborhood, which still show Lithium in their atmosphere.
I will discuss the results of the orbital fits, including the first dynamical mass estimate of the Kelu-1 AB system. The analysis seems to confirm the already previously reported trend that current evolutionary and atmospheric models tend to underestimate the mass of very-low-mass stars and brown dwarfs.
Alternatively, additional spatially resolved system components (i.e. a higher degree of multiplicity) could explain the surprisingly high dynamical mass estimates. In the case of Kelu-1 AB, we indeed found spectroscopic evidence for a third, previously undetected, system component, which resolves the apparent discrepancy between evolutionary models and dynamical mass estimates. This makes Kelu-1 AB the first pure brown dwarf triple system discovered so far.
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