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White Dwarfs in Common Proper Motion Binary Systems: Mass Distribution and Kinematics
We present the mass distribution, gravitational redshifts, radialvelocities, and space motions of white dwarf stars in common propermotion binary systems. The mass distribution we derive for the 41 DAwhite dwarfs in this study has a mean of 0.68+/-0.04 Msolar.This distribution has a slightly higher mean and larger dispersion thanmost previous white dwarf studies. We hypothesize that this is due to ahigher fraction of cool (average Teff~10,000 K), hence old,white dwarfs in our sample. Our results indicate that samples made up ofpredominantly cool, old white dwarf stars tend to have a bimodaldistribution with a second mass peak at ~1.0 Msolar, whichskews the mean toward a higher mass. Both the mean and individual whitedwarf masses we report here are in better agreement with thosedetermined from model atmosphere spectroscopic fits to line profilesthan with most previous gravitational redshift studies of cool whitedwarfs. Our results indicate that measurement biases and weak geocoronalemission lines in the observed spectra may have affected previousgravitational redshift measurements. These have been minimized in ourstudy. We present measurements for some previously unobserved whitedwarfs, as well as independent new measurements for some that have beenreported in the literature. A list of complete space motions for 50 widebinary white dwarfs is presented, derived from radial velocitymeasurements of their nondegenerate companions. We find that the UVWspace motions and dispersions of the common proper motion binaries thatcontain white dwarf components are consistent with those of old,metal-poor disk stars.
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