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Published online by Cambridge University Press: 12 April 2016
Alcock (1979a,b) has suggested that DB degenerate dwarfs can only be kept observably free of accreted interstellar hydrogen if their masses are not more than about 0.3 M⊙. This is distressing because (a) photometrically determined DB radii (hence masses) are not statistically different from those of DA’s (Shipman 1979), and (b) no one quite knows how to make a degenerate dwarf with this low a mass in the age of the galaxy. Several authors (Vauclair et al. 1979; Michaud and Fontaine 1979) have suggested that accretion is inhibited by effects of coronae and/or magnetic fields. I address here the possibility that the DB’s are a somewhat higher velocity population than the general run of degenerate dwarfs. Although, as we shall see, this may imply somewhat lower than average masses for them, the dominant effect will be reduced accretion due to the high speed of the stars through the interstellar gas.