Physics – Optics
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21421104d&link_type=abstract
American Astronomical Society, AAS Meeting #214, #211.04; Bulletin of the American Astronomical Society, Vol. 41, p.717
Physics
Optics
Scientific paper
We are conducting an orbital monitoring program to determine the dynamical masses of brown dwarf binaries using Keck laser guide star adaptive optics (LGS AO). With orbital periods of 5-15 years, the binaries most likely to yield masses in a reasonable time frame have the smallest separations (50-100 mas). Keck LGS AO is ideal for monitoring these binaries because of its exceptional resolving power, routinely achieving diffraction-limited images in the near-infrared. This is crucial for determining precise masses, as the mass precision is very sensitive to the measured angular separation (α3). Mass measurements for brown dwarfs are critical for testing substellar theoretical models, which are widely used but have been largely unconstrained by observations. We have recently measured the dynamical mass of the L4+L4 binary HD 130948BC to be 114±2 MJup, and since it is in a hierarchical triple with a young solar analog (G2V) its age is also well constrained (0.8±0.2 Gyr). These are now the first substellar field dwarfs with luminosity, mass, and age measurements, enabling a direct test of evolutionary models. Surprisingly, both components appear to be overluminous by a factor of 2-3 compared to the models. This would have wide-ranging implications as, for example, these models are used to predict the luminosity and radius evolution of extrasolar giant planets. Along with our recent dynamical mass measurement of the T dwarf binary 2MASS J1534-2952AB, our ongoing orbital monitoring program with Keck LGS AO has already doubled the number of brown dwarfs with mass determinations. Forthcoming results will provide mass measurements for brown dwarfs in the L/T transition for the first time. These will provide strong observational constraints on perhaps the most complex phase of substellar evolution in which dust clouds are rapidly replaced by molecular species (e.g., CH4) as the dominant opacity source in ultracool atmospheres.
Dupuy Trent J.
Ireland Michael J.
Liu Michael C.
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