LOW-MASS BINARIES IN THE HYADES

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