PHOTOMETRIC BINARY STARS IN PRAESEPE AND THE SEARCH FOR GLOBULAR-CLUSTER BINARIES

A radial velocity study of the stars which are located on a second sequence above the single-star zero-age main sequence at a given color in the color-magnitude diagram of the open cluster Praesepe (= M44, NGC 2632) shows that 10, and possibly 11, of 17 are binary systems. Of the binary systems, five have full amplitudes for their velocity variations that are greater than 50 km s-1. To the extent that they can be applied to globular clusters, these results suggests that (1) observations of "second-sequence" stars in globular clusters would be an efficient way of finding main-sequence binary systems in globulars, and (2) current instrumentation on large telescopes is sufficient for establishing unambiguously the existence of main-sequence binary systems in nearby globular clusters.