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| Paper: |
Testing Theory with Dynamical Masses and Orbits of Ultracool Binaries |
| Volume: |
448, 16th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun |
| Page: |
111 |
| Authors: |
Dupuy, T. J.; Liu, M. C.; Ireland, M. J. |
| Abstract: |
Mass is the fundamental parameter that governs the evolution of
stars, brown dwarfs, and gas-giant planets. Thus, direct mass
measurements are essential to test the evolutionary and atmospheric
models that underpin studies of these objects. We present results
from our program to test models using precise dynamical masses for
visual binaries based on Keck laser guide star adaptive optics
astrometric monitoring of a sample of over 30 ultracool (> M6) objects since 2005. In just the last 2 years, we have more
than tripled the number of late-M, L, and T dwarf binaries with
precise dynamical masses. For most field binaries, based on direct
measurements of their luminosities and total masses, we find a
“temperature problem” in that evolutionary model radii give
effective temperatures that are inconsistent with those from model
atmosphere fitting of observed spectra by 100–300 K. We also find
a “luminosity problem” for the only binary with an independent age
determination (from its solar-type primary via
age–activity–rotation relations). Evolutionary models
underpredict the luminosities of HD 130948BC by a factor of
≈2, implying that model-based substellar mass determinations
(e.g., for directly imaged planets and cluster IMFs) may be
systematically overestimating masses. Finally, we have employed the
current sample of binary orbits to carry out a novel test of the
earliest evolutionary stages, by using the distribution of orbital
eccentricities to distinguish between competing models of brown
dwarf formation. |
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