A Search for Spectroscopic Binaries in NGC 3201

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Session 50 -- Globular Clusters
Display presentation, Wednesday, 9:20-6:30, Pauley Room

[50.01] A Search for Spectroscopic Binaries in NGC 3201

P. C\^ot\'e, D.L. Welch, P. Fischer (McMaster), G.S. Da Costa (AAO), P. Tamblyn (Steward), P. Seitzer (Michigan), M.J. Irwin (RGO)

$B,V$ CCD and APM photometry, accurate astrometry and 1859 radial velocities have been obtained for 1318 stars within $\sim$ 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 16 known NGC 3201 photometric variables in our sample, we have a database of 938 radial velocities for 423 member giants with which to identify spectrocopic binaries on the basis of radial velocity variations. The mean time span of the observations is 1.7 years, with coverage up to about 6 years 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 $\le P \le$ 5 -- 10 years and mass ratios in the range 0.1 -- 1) of 0.07 -- 0.10 (circular orbits) and 0.10 -- 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 sample of other globular clusters (0.05 -- 0.12) studied by Hut $et~al.$ 1992, PASP, 104, 981.

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