Physics – Optics
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...212.1106d&link_type=abstract
American Astronomical Society, AAS Meeting #212, #11.06; Bulletin of the American Astronomical Society, Vol. 40, p.204
Physics
Optics
Scientific paper
Brown dwarfs are of keen interest to many areas of astronomy as objects that bridge the gap between planets and stars. For substellar objects in the field, the fundamental property of mass has been measured for only a few systems (e.g., Gl 802Bab and 2MASS J1534-2952AB). None of these has a independent age estimate, which is the other key deterministic property of brown dwarfs since they cool and dim over time, never reaching a main-sequence. We present orbital monitoring of HD 130948BC using Keck Natural Guide Star Adaptive Optics (NGS AO), along with a new analysis of archival HST and Gemini AO data. With 70% coverage of the 10-year orbit, we determine a total mass of 114±2; MJup. With a near-unity mass ratio, both objects are unambiguously substellar. Since these substellar objects are part of a triple system, the G2V primary HD 130948A provides an independent age constraint for the substellar members. The age estimated for the primary star is consistent with that inferred from evolutionary models. However, Lyon and Tucson models predict very different levels of lithium depletion in B and C, since the mass of B is very close to the theoretical lithium-burning limit and the age of the system is close to the theoretical onset lithium burning. Thus, future measurements of lithium absorption in HD 130948BC with resolved optical spectroscopy (i.e., the "binary lithium test") will provide a strongly discriminating test of evolutionary models. The effective temperatures of B and C (1900-2000 K) also appear to be inconsistent with spectral synthesis modeling for objects of the same spectral type using state-of-the-art atmospheric models (1700-1800 K). As the only substellar binary with a directly measured dynamical mass and independent age constraint, HD 130948BC is a key benchmark system for constraining evolutionary and atmospheric models of ultracool dwarfs.
Dupuy Trent J.
Ireland Michael J.
Liu Michael C.
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