Stellar atmosphere models available at

http://ams.astro.univie.ac.at/nemo/

  Nice example of binary star with brown dwarf, calc mass

http://www.eso.org/outreach/press-rel/pr-2004/pr-16-04.html

  Using astrometry _and_ radial velcity measurements
to figure out mass of planet in Gliese 876:

      http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2002ApJ...581L.115B&db_key=AST&data_type=HTML&format=&high=3f6510b0d829772