Microlensing Discovery of a Population of Very Tight, Very Low-mass Binary Brown Dwarfs

dF star Number of posts : 3337 Registration date : 2008-06-12

Microlensing Discovery of a Population of Very Tight, Very Low-mass Binary Brown Dwarfs
http://arxiv.org/abs/1302.4169

OGLE-2009-BLG-151/MOA-2009-BLG-232L
Primary: 0.018 ± 0.001 solar masses
Secondary: 0.0075 ± 0.0003 solar masses

OGLE-2011-BLG-0420L
Primary: 0.025 ± 0.001 solar masses
Secondary: 0.0094 ± 0.0005 solar masses

Both of the secondaries have mass estimates well below the "canonical" deuterium fusion limit of 13 Jupiter masses.

Quote :: Although many models have been proposed, the physical mechanisms responsible for the formation of low-mass brown dwarfs (BDs) are poorly understood. The multiplicity properties and minimum mass of the BD mass function provide critical empirical diagnostics of these mechanisms. We present the discovery via gravitational microlensing of two very low mass, very tight binary systems. These binaries have directly and precisely measured total system masses of 0.025 M ☉ and 0.034 M ☉, and projected separations of 0.31 AU and 0.19 AU, making them the lowest-mass and tightest field BD binaries known. The discovery of a population of such binaries indicates that BD binaries can robustly form at least down to masses of ~0.02 M ☉. Future microlensing surveys will measure a mass-selected sample of BD binary systems, which can then be directly compared to similar samples of stellar binaries.

http://arxiv.org/abs/1302.4169

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