1. Provide precise (sigma < 0.5 km/sec) stellar radial velocities to V=17 in order to establish cluster membership and internal motions.
2. Obtain orbit solutions for all cluster binary stars with periods of less than 1000 days, in order to study binary populations, stellar evolution, and cluster dynamics.

NGC 188: We have obtained 6432 precise radial velocity measurements of 512 stars over 8 years, revealing 146 binaries and providing 90 orbit solutions. The resulting eccentricity-log period diagram definitively shows tidal circularization progressing with time for main-sequence binaries older than 1 Gyr, a critical test between competing theories (Mathieu, Meibom & Dolan 2003; WOCS XVIII, Geller et. al., in draft ).

NGC 6819: This cluster is well placed in age for tests of convective overshoot and helium ignition. We have underway a radial-velocity survey of a photometrically selected sample in a 12' (10 pc) radius. We have 5140 measurements of 1140 stars, identified 524 members and obtained 36 binary orbit solutions. These data have revealed the giant branch and the detailed structure of the turnoff (Hole, Mathieu & Latham, submitted ).

NGC 1039, M35, and NGC 2264: We have obtained 2600 measurements of 487 stars in NGC 1039 (M34), 5095 measurements of 1276 stars in NGC 2168 (M35), and 2288 measurements of 358 stars in NGC 2264. We have orbit solutions for 17 binaries in NGC 1039, 42 binaries in NGC 2168, and 6 binaries in NGC 2264. The paucity of binaries in NGC 2264 is not due to limited observation; the low frequency is real and even more marked for the shortest period binaries. Analyses of these data are underway (Meibom & Mathieu, in draft.).

Other Clusters:

A radial velocity surveys are also underway for NGC 6633, in collaboration with Deliyannis.

New WOCS target clusters for 2004-2006:

NGC 2506, NGC 2682, NGC 6791 and NGC 7789 (see Astrometry link for more information), to be done in collaboration with Latham and Torres using the new Hectochelle at the MMT.

The primary facility is the WIYN 3.5m telescope and Multi-Object Spectrograph. The MOS consists of the Hydra positioner, which in 20 minutes can place 89 fibers within the 1-degree diameter focal plane of the telescope to ~ 0.2 arcsec precision. This project employs the 3-arcsec diameter blue-optimized fiber bundle. The fibers feed a bench-mounted spectrograph in a thermally isolated room. With the echelle grating and Bench Spectrograph Camera the system produces a resolution of 20,000 at 5100 Å. The wavelength coverage of 200 Å around the central wavelength of 5100 Å provides a rich array of narrow absorption lines in addition to the Mg B triplet. With an order separation filter up to 89 spectra are obtained simultaneously. The Bench Spectrograph Camera has no obstruction for high throughput; a 7200-sec integration in typical conditions provides a S/N ~ 15 at V=16. These spectra straightforwardly achieve radial-velocity measurement precisions of 0.4 km/sec.