THE HYADES SUPERCLUSTER IN THE FK5

The members of the Hyades supercluster brighter than about M(V) = +4 mag and contained in the FK5, or having nearly FK5 quality proper motions, show a convergent point of (A,D) = (6.h, + 6.5-degrees). The Hyades cluster stars in the FK5 have a mean distance of 46.7 pc (modulus=3.35 mag). The supercluster, as well as the Hyades and Praesepe cluster, populations represent at least three age groups. Because of difficulties with the temperature-to-color conversion, and the possibility that the stellar cores have convective overshoot, precise dating is impossible but, presumably, these problems will not affect differential age determinations. Standard models indicate ages of 3 to 4, 6, and 8 X 10(8) yr, whereas model ages with convective overshoot are nearly twice this. Most of the Am and USPC (delta Sct) stars in the supercluster are of the same age (approximately 8 X 10(8) yr for standard models). The Ap stars mark the onset of shell hydrogen burning. The photometry of the red giants confirms the age spread and indicates a weakening of CN strength with age. Attention is called to the need for further study of NGC 2423 as an effective prolusion to understanding the evolution of the supercluster.