2002AJ....124.1118S

We present measured radial velocities and complete space motions for 116 white dwarf stars with M dwarf companions. Thirteen pairs have ``halo-like'' velocities. According to a recent study by Oppenheimer et al., all these high-velocity white dwarfs should be considered part of the dark matter heavy halo of the Galaxy, based on their kinematics. Based on the near-solar abundance levels of the M dwarf companions, we conclude that 12 of our 13 high-velocity white dwarfs are actually part of the high-velocity tail of the thick disk, rather than the dark matter halo of the Galaxy, in agreement with the results of a recent study of 514 M dwarfs performed by Reid, Sahu, & Hawley. We find only one potential stellar halo white dwarf (LP 164-52) in our sample. The M dwarf companion of LP 164-52 is a metal-poor, intermediate subdwarf with high-velocity UVW-space motions. In view of the similarity to our sample, we conclude that the majority of the dark matter halo white dwarfs identified by Oppenheimer et al. are most likely to be members of the thick disk, and hence their contribution to the dark matter content of the halo is very much overestimated. Our results suggest that the assignment of population membership solely on incomplete kinematical information is not definitive and that a more robust examination of suspected halo white dwarfs must be performed.