Stellar masses, kinematics, and white dwarf composition for three close DA plus dMe binaries

We determine the mass functions and mass ratios for three close white dwarf plus red dwarf binaries (EUVE J0720-317, 1016-053,and 2013+400). Hubble Space Telescope Goddard High-Resolution Spectrograph spectra of the He II lambda 1640 and C IV lambda 1550 spectral lines trace the white dwarf orbital motion, and Hamilton Spectrograph echelle spectra (Lick Observatory) and lower dispersion spectra trace the red dwarf orbital motion. The data sets allow us to measure orbital periods and velocities, as well as the white dwarf gravitational redshifts. The red dwarf and white dwarf mass estimates obtained from a combination of independent mass measurements for the white dwarf stars and our new orbital elements help constrain probable evolutionary outcomes. We find that EUVE J0720-317 will probably come into contact within a Hubble time and that the mass transfer will be unstable on a dynamical time. We also conclude that the much lower secondary masses in EUVE J1016-053 and EUVE J2013+400 exclude the possibility of significant interaction in these systems. We also present new helium and carbon photospheric abundance measurements in the three white dwarfs. The white dwarf atmospheric composition may show the effects of accretion of red dwarf mass-loss material onto its surface. Finally, we study the kinematics of the systems, and we also show that the white dwarf in EUVE J1016-053 is part of a quadruple system.