The Parentage of Magnetic White Dwarfs: Implications from Their Space Motions

We have examined the statistical properties, cooling ages, and vector components of the three-dimensional space motion U, V, W for the enlarged sample of 53 magnetic white dwarfs contained in the fourth edition of the Catalog of Spectroscopically Identified White Dwarfs (McCook & Sion). Their cooling ages range from 2 million years to 12.6 billion years. A comparison of the total kinematic samples of magnetics and DA stars over the same luminosity range 10.0 < M-v < 16.0 reveals a velocity dispersion sigma(v) = 39 km s(-1) for 256 DA stars compared with sigma(v) = 23 km s(-1) for 26 magnetic degenerates with space motions. These results underscore the conclusion that the sample of magnetic white dwarfs appears to be predominantly descended from a young disk stellar population subcomponent characterized by relatively small motions with respect to the Sun. This suggests both links to upper main-sequence Ap/Bp progenitors but possibly also massive "near miss " pulsar progenitors. We find preliminary evidence that the magnetic white dwarfs show a peculiar distribution in UV velocity space relative to other spectroscopic subgroups of white dwarfs. However, there is little evidence of a difference in velocity dispersion among the hot and cool magnetic degenerates, despite their having vastly different cooling ages. This may be taken as indirect evidence that the magnetics represent a sample of mixed evolutionary progeny.