LOW-MASS BINARIES IN THE HYADES

We have used the HST Planetary Camera to search for companions to a sample of low-mass (M(nu)>11.5) members of the Hyades cluster. Our observations, which extend in sensitivity beyond the hydrogen-burning limit, detect 5 companions amongst the 21 targets. One binary system appears to Lie 70% beyond the Hyades, so the observed binary fraction is 20%+/-10%. If the distribution of orbital parameters is similar to that of higher mass stars, this implies an overall binary fraction of 27%+/-16%. Our result for the Hyades is in good agreement with analysis of the 5.3 pc nearby star sample, but is significantly lower than the binary fractions observed amongst similar to 1M(circle dot) main-sequence stars (similar to 60%) and T Tauri stars (>70%). (C) 1995 American Astronomical Society.