Preliminary Physical Orbit of the HD 98800 B System
          Andy Boden, MSC/Caltech
          Anneila Sargent, Caltech
          Rachel Akeson, MSC/Caltech
          John Carpenter, Caltech
          Guillermo Torres, Harvard-CfA
          David Latham, Harvard-CfA
          David Soderblom, STScI

          As a part of a larger program to measure physical properties of PMS binary systems, we have observed the PMS quadruple system HD 98800  (aka TW Hya 4A) with the Keck Interferometer (KI), and resolved the two separate spectroscopic binary components of the system.  In particular we have observed the HD 98800 North (B) binary component on multiple epochs, and integrating our data with the double-lined spectroscopic orbit from Torres et al 1995 has allowed us to estimate a physical orbit for the B system.  This orbit in turn yields relatively accurate (5%) mass estimates of the component stars, and an independent system distance and component luminosity estimates.  Our orbital solution favors a high-inclination orientation for the orbit, suggesting that both components of the HD 98800 B system are under 0.6 Msolar. Comparisons between the estimated physical parameters for the HD 98800 B components with mass-luminosity models of PMS stars, and implications for the age of HD 98800 and the TW Hya association will be discussed.