White Dwarfs in Common Proper Motion Binary Systems: Mass Distribution and Kinematics

Abstract

We present the mass distribution, gravitational redshifts, radial velocities, and space motions of white dwarf stars in common proper motion binary systems. The mass distribution we derive for the 41 DA white dwarfs in this study has a mean of 0.68^0.04 This distribution has a slightly higher mean M _. and larger dispersion than most previous white dwarf studies. We hypothesize that this is due to a higher fraction of cool (average K), hence old, white dwarfs in our sample. Our results T eff D 10,000 indicate that samples made up of predominantly cool, old white dwarf stars tend to have a bimodal distribution with a second mass peak at D1.0 which skews the mean toward a higher mass. Both M _ , the mean and individual white dwarf masses we report here are in better agreement with those determined from model atmosphere spectroscopic Ðts to line proÐles than with most previous gravitational redshift studies of cool white dwarfs. Our results indicate that measurement biases and weak geocoronal emission lines in the observed spectra may have a †ected previous gravitational redshift measurements. These have been minimized in our study. We present measurements for some previously unobserved white dwarfs, as well as independent new measurements for some that have been reported in the literature. A list of complete space motions for 50 wide binary white dwarfs is presented, derived from radial velocity measurements of their nondegenerate companions. We Ðnd that the UV W space motions and dispersions of the common proper motion binaries that contain white dwarf components are consistent with those of old, metal-poor disk stars.

Spectroscopic and photometric studies of white dwarfs in the Hyades

“…The first is the DA WD 0120−024 (No. 11), which has only been fitted using the V − I color in Silvestri et al (2001). On the contrary, our data set includes 2MASS JHK S photometry, and we could also find for this object the Johnson BVRI photometry (Smith 1997).…”

“…Our fit is shown in Fig. 2 with the gravity fixed at the value found by Silvestri et al (2001) from a gravitational redshift measurement. We note a discrepancy at the K S band, which is not unusual as it is close to the detection limit of 2MASS.…”

Testing the Initial–Final Mass Relationship of White Dwarfs

“…Particularly, WD1750+098 turned out to be of type DC although in the last reference in the literature (Silvestri et al 2001) it was classified as a DA. We believe that WD1544+008 is the same star as WD1544+009, which was classified as a DAB white dwarf by Silvestri et al (2001). However, it was identified as a sdO star by Wegner & Reid (1991).…”

“…The sample of common proper motion pairs to be observed was chosen from the available literature, mainly from the papers of Silvestri et al (2001) and Wegner & Reid (1991), and from a cross-correlation of the SIMBAD database and the Villanova White Dwarf Catalog. We selected the pairs taking into account several requirements.…”

Catalogs of Wide Binaries: Impact on Galactic Astronomy

“…• measurement of the masses of white dwarfs and constraints on the (dark) mass density of stellar remnants in the local Galactic disk (Silvestri et al 2001);…”