The dynamical determination of the masses of young stars and brown dwarfs will be continued through an extensive observational program using a variety of tools and techniques. The work is motivated by substantial uncertainties in theoretical mass relations for substellar masses, the lack of empirical calibrations (temperature, luminosity, etc.) for very low mass/young stars, and uncertainties the distribution of mass ratios in clusters. The goal is to obtain dynamical masses to within 10% for stars of mass 1 to 0.5 that of the Sun, and to within 20% for those of even less mass. Four specific projects will be undertaken: 1) The orbits of young visual binaries, including low mass pre-main sequence stars, will be improved using Keck and Gemini Observatory laserguide star Adaptive Optics systems and Hubble Space telescope Fine Guidance Sensor observations. 2) The mass ratio distribution in the Hyades will be explored using the Infrared Telescope Facility and the Cryogenic Echelle Spectrograph to observe spectroscopic binaries. 3) Masses of two pre-main sequence stars will be improved by observing the rotation of circumstellar disks in the 13CO line where the ambient cloud brightness should be lower (extended emission from the cloud was a source of uncertainty in previous 12CO measurements). 4) The dynamical masses of brown dwarfs will be determined from observations of brown dwarf binaries, which will be used to test theoretical mass-luminosity relations. This work will directly support the training of graduate students in contemporary instrumentation and collaborative investigations. Both students in the NSF supported Research Experiences for Undergraduates program at Stony Brook and Stony Brook undergraduates will also participate through independent research projects. Results of the work will be disseminated to the public through an ongoing monthly "Open Nights in Astronomy" program and talks to local amateur astronomy groups.
