The Incidence of Close Binaries among Stars of Low Mass: Astrophysical Binaries

Using a single-stage Varo image tube at the coude spectrograph of the Lick Observatory, the authors obtained multiple spectrograms of 48 dM stars and 15 dMe stars, centered at H-alpha, with a reciprocal dispersion of about 17 A/mm. The results of precise measurements of the radial velocities of these stars, and of an analysis to search for low-amplitude binaries in the sample are reported. Evidence for two new binaries is found in the sample of dMe stars, and none in the sample of dM stars. It is argued that it may not be possible for an M-dwarf star to be a component in a binary system with a period of less than 5 d without being so active as to produce Balmer line emission. The Galactic kinematics of the sample is displayed, giving further support to the notion that the dMe stars may be a young subset of all M dwarfs, and further suggesting that they may all be associated with the Pleiades supercluster.