A SEARCH FOR BINARIES IN THE GLOBULAR-CLUSTER NGC-3201

We present BV CCD and APM photometry, accurate astrometry and 1859 radial velocities for 1318 stars within approximately 36' of the Galactic globular cluster NGC 3201. The field and cluster populations separate unambiguously in two distinct samples since the systemic radial velocity of NGC 3201 is 494.2 km s-1. After removal of the 19 known NGC 3201 photometric variables in our sample, we have a database of 930 radial velocities for 420 member giants (276 of which have multiple velocity measurements) with which to identify spectroscopic binaries on the basis of radial velocity variations. The mean time span of the observations is 1.7 yr, with coverage up to approximately 6 yr for our best-studied stars. Monte Carlo simulations of the observed velocity variations have provided upper limits to the cluster binary fraction (for binaries with 0. 1 less-than-or-equal-to P less-than-or-equal-to 5-10 yr and mass ratios in the range 0.1 - 1) of 0.06-0.10 (circular orbits) and 0. 15-0.18 (eccentric orbits). These results suggest an incidence of binarism for NGC 3201 consistent with the corresponding incidence among nearby solar-type stars having similar periods and mass ratios (0.04-0.08) and that for a small sample of other globular clusters (0.05-0.12) studied by Hut et-al. (1992).