Testing theory with dynamical masses and orbits of ultracool binaries

Trent J. Dupuy*, Michael C. Liu, Michael J. Ireland

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference proceeding contribution

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.

Original languageEnglish
Title of host publicationThe 16th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun
Subtitle of host publicationproceedings
EditorsChristopher M. Johns-Krull, Matthew K. Browning, Andrew A. West
Place of PublicationSan Francisco, CA
PublisherAstronomical Society of the Pacific
Pages111-118
Number of pages8
ISBN (Electronic)9781583817773
ISBN (Print)9781583817766
Publication statusPublished - 2011
Externally publishedYes
Event16th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun - Seattle
Duration: 28 Aug 20103 Sep 2010

Publication series

NameAstronomical Society of the Pacific conference series
PublisherAstronomical Society of the Pacific
Volume448

Conference

Conference16th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun
CitySeattle
Period28/08/103/09/10

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