AAS 197, January 2001
Session 41. Star Clusters and Associations
Display, Tuesday, January 9, 2001, 9:30am-7:00pm, Exhibit Hall

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[41.05] WIYN Open Cluster Study: Precise Radial Velocities of Stars in the Old Cluster NGC 188

S.C.D. Meibom, S.A. Barnes, C.J. Dolan, R.D. Mathieu (University of Wisconsin - Madison)

We have used the WIYN 3.5m telescope and Hydra Multi-Object Spectrograph since 1996 to obtain precise radial velocities for late-type proper-motion members of the open cluster NGC 188. Our magnitude limit of V < 16.5 includes solar-mass main-sequence stars, subgiants and giants, and blue stragglers. The survey includes a 0.75 deg diameter area on the sky.

At present, the radial-velocity database contains over 5000 observations of more than 500 stars. The standard deviation of measurements for a representative single cluster member is 0.45 km/s and drops to 0.3 km/s for the brightest stars. The latter is the result of equal contributions from night-to-night variations of 0.2 km/s and fiber-to-fiber variations of 0.2 km/s. Comparison with an ongoing radial-velocity study at DAO by Harris and McClure indicates a 0.3 km/s difference in zero-point that remains to be resolved.

More than 75 stars are confirmed spectroscopic binaries or candidate radial velocity variables; orbital solutions have been obtained for 52 of these. We will present results on mass segregation of the binaries, the tidal circularization cutoff, the short-period binary frequency, a newly discovered sub-subgiant binary, and the blue straggler binary population.

This work is supported by NSF AST 9731302.

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