1999AJ....117..343R

We have used both the Low-Resolution Imaging Spectrograph and the High Resolution Echelle Spectrograph on the Keck telescopes to obtain spectra of 12 candidate members of the Hyades identified by Leggett & Hawkins. All of the objects are chromospherically active, late-type M dwarfs, with Hα equivalent widths varying from 1 to 30 Å. Based on our measured radial velocities, the level of stellar activity, and other spectroscopic features, only one of the 12 stars has properties consistent with cluster membership. We consider how this result affects estimates of the luminosity and mass function of the Hyades. Five of the 11 field stars have weak K I λλ7665, 7699 and CaH absorption as compared with M dwarf standards of the same spectral type, suggesting a lower surface gravity. Two of these sources, LH 0416+14 and LH 0419+15, exhibit significant lithium 6708 Å absorption. Based partly on parallax measurements by the US Naval Observatory (Harris et al.), we identify all five as likely to be young, pre-main-sequence objects in or near the Taurus-Auriga association at distances of between 150 and 250 pc. A comparison with theoretical models of pre-main-sequence stars indicates masses of less than 0.05 M_☉.