  We report on Keck Interferometer observations of the double-lined binary (B)
component of the quadruple pre-main sequence (PMS) system HD 98800. With these
interferometric observations combined with astrometric measurements made by the
Hubble Space Telescope Fine Guidance Sensors (FGS), and published radial
velocity observations we have estimated preliminary visual and physical orbits
of the HD 98800 B subsystem. Our orbit model calls for an inclination of 66.8
$\pm$ 3.2 deg, and allows us to infer the masses and luminosities of the
individual components. In particular we find component masses of 0.699 $\pm$
0.064 and 0.582 $\pm$ 0.051 M$_{\sun}$ for the Ba (primary) and Bb (secondary)
components respectively.
  Modeling of the component SEDs finds temperatures and luminosities in
agreement with previous studies, and coupled with the component mass estimates
allows for comparison with PMS models in the low-mass regime with few empirical
constraints. Solar abundance models seem to under-predict the inferred
component temperatures and luminosities, while assuming slightly sub-solar
abundances bring the models and observations into better agreement. The present
preliminary orbit does not yet place significant constraints on existing
pre-main sequence stellar models, but prospects for additional observations
improving the orbit model and component parameters are very good.
