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G. F. Benedict, B.E. McArthur (McDonald Obs., U. Texas), O.G. Franz, L.H. Wasserman (Lowell Obs.), T. J. Henry (Harvard-SAO), Tsunenori Takato (Astronomy, U. Texas), Iskra Strateva (Astronomy, Princeton), E. Nelan (STScI), W.H. Jefferys (Astronomy, U. Texas), R.L. Duncombe (Aerospace Eng., U. Texas), P.J. Shelus (McDonald Obs., U. Texas), P.D. Hemenway (U. Rhode Island), D. Story (Jackson & Tull), A.L. Whipple, A. Bradley (Allied-Signal Aerospace), Wm. van Altena (Astronomy, Yale U.), L.W. Fredrick (Astronomy, U. Virginia)
We present mass determinations for two low-mass binary systems, Gl 623AB and Wolf 1062 (Gl 748AB). Both systems have been observed with Fine Guidance Sensor 3, one of the white-light interferometers aboard Hubble Space Telescope. We have carried out a parallel ground-based radial velocity investigation utilizing the Sandiford Echelle Spectrograph (McCarthy et al. 1993. PASP, 105, 881) at the McDonald Observatory 2.1m telescope. For Gl 623 we use radial velocity data from Marcy & Moore (1989. ApJ, 341, 961) and our program to augment the sparse HST astrometry (less than a complete orbit) and derive preliminary masses. The error in the mass of Gl 623B has been reduced by a factor of three over that used for the Henry et al. (1999. ApJ, 512, 864) Mass-Luminosity Relation. Having obtained a complete wrap of the orbit for Gl 748 with our HST observations (Franz et al. 1998. AJ, 116, 1432), we use the radial velocities to obtain an independent check of the parallax.
We review the Mass-Luminosity Relation using masses from the above two systems, along with Gl 791.2AB and preliminary masses for Wolf 922 (Gl 831AB).
This work was supported by NASA HST GTO Grant NAG5-1603 and STScI GO grants GO-06882, GO-07491, and GO-07493.