Low-Mass Binaries in the Hyades

Abstract

We have used the HST Planetary Camera to search for companions to a sample of low-mass (M_υ > 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 ∼1 M_sunmain-sequence stars (∼60%) and T Tauri stars (>70%).