THE ASTROPHYSICAL JOURNAL, 490:328, 1997 November 20

        THE "MASS DISCREPANCY" FOR MASSIVE STARS: TESTS OF MODELS USING
                            SPECTROSCOPIC BINARIES

                              VALORIE BURKHOLDER
       Department of Physics and Astronomy, Northern Arizona University,
       P. O. Box 6010, Flagstaff, AZ 86011-6010; veburkho@mtholyoke.edu

                                 PHILIP MASSEY
   Kitt Peak National Observatory, National Optical Astronomy Observatories,
            P. O. Box 26732, Tucson, AZ 85726-6732; massey@noao.edu

                                      AND

                                 NIDIA MORRELL
     Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional
            de La Plata, Argentina; nidia@fcaglp.fcaglp.unlp.edu.ar


                                   ABSTRACT

        Stellar evolutionary models are often used to infer a star's mass
     via its luminosity, but empirical checks on the accuracy of the
     theoretical mass-luminosity relation for very massive stars have been
     lacking.  This is of particular concern given that modern atmosphere
     models yield systematically smaller masses for massive stars than do
     evolutionary models, with the discrepancy a factor of two for Of
     stars.  We attempt to resolve this mass discrepancy by obtaining new,
     high-resolution optical data on seven early-type spectroscopic
     binaries: V453 Cyg, HD 191201, V382 Cyg, Y Cyg, HD 206267, DH Cep, and
     AH Cep.  Our study produces improved spectral substypes for the
     components of these systems, crucial for evaluating their luminosities
     and locations in the H-R diagram.  Our radial velocity study utilizes
     a measuring method which explicitly accounts for the effects of
     pair-blending.  We combine our new orbit solutions with existing data
     on inclinations and distances when available to compare the orbital
     masses with evolutionary models, and we find good agreement in all
     cases where the stars are non-interacting. (The components of V382 Cyg
     and DH Cep fill their Roche lobes, and in both cases we find masses
     substantially lower than the masses inferred from evolutionary tracks,
     suggesting that significant material has been lost rather than
     transferred.  We confirm that this same trend exists for other systems
     drawn from the literature.)  Our own data extends to only 15 Msun,
     although photometric inclination determinations for HD 191201 and HD
     206267 should prove possible, and will provide examples of higher mass
     systems.  We briefly discuss suitable systems from the literature, and
     conclude that orbit solutions provide good agreement with the
     evolutionary models to 25 Msun. Beyond this, most known binaries
     either fill their Roche lobes or have other complications.  We also
     discuss five systems for which our improved data and analysis failed
     to yield acceptable orbit solutions: EO Aur, IU Aur, V640 Mon
     (Plaskett's star), LY Aur, and 29 UW CMa all remained intractable,
     despite improved data.

     Subject headings: binaries: spectroscopic -- stars: early-type --
                       stars: evolution -- stars: fundamental parameters