THE LOW-MASS HYADS AND THE EVAPORATION OF CLUSTERS

The 135 single stars and 85 binary systems, redder than R - I = + 0.34 mag and brighter than V = 17 mag, between alpha = 3.75h and 5.0h and delta = + 5-degrees and + 25-degrees show a luminosity function that differs considerably from that of the general field stars within 20 pc of the Sun. The ratio of double star components to single cluster members increases markedly with decreasing luminosity. Forty-three single stars and 16 binary systems that are members of the Hyades supercluster within 20 pc of the Sun show the same luminosity function as the field stars in that region. Fifty percent of the cluster members and 40 percent of the supercluster members are components of binary stars. The equivalent widths of Ha appear to support a range of ages (approximately 8 to 16 X 10(8) yr) for the cluster stars and demonstrate that the oldest objects are in the supercluster. A list of cluster members, which may include the end of the stable main sequence, but for which accurate (R - I) photometry is not available, is included. The half-dozen known parallax stars of the faintest luminosity contain at least one supercluster member, TVLM 868-110639, which is probably beyond the stable, nuclear burning main sequence as a ''transitional'' or ''brown'' dwarf.