Radial-Velocity Measurements and Spectroscopic Binary Orbits in the Open Cluster NGC 7789

We introduce the first comprehensive catalog of the hard binary population studied in the rich open cluster NGC 7789 (1.6 Gyr, [Fe/H] = +0.02). Our sample consists of 1206 photometrically selected stars drawn from the upper main sequence and evolved stellar population of NGC 7789, which includes giants, red-clump stars, blue stragglers, red stragglers, and sub-subgiants. Our survey, as part of the ongoing WIYN Open Cluster Study (WOCS), began in 2005 and comprises more than 9,000 time-series radial-velocity measurements from the Hydra Multi-Object Spectrograph on the WIYN 3.5m telescope. We derive RV membership probabilities, and in conjunction with high-precision astrometry obtained from Gaia DR2, we are able to identify 564 likely cluster members and fit orbital solutions for 83 cluster binary stars with periods between 1.45 d and 4200 d, including four blue stragglers. From this catalog we investigate key cluster properties such as binary frequency and tidal circularization period. These data are a foundation for future dynamical studies of intermediate-age, densely populated open clusters such as NGC 7789. The authors acknowledge funding support from NSF AST-1714506. The authors also gratefully acknowledge the many Wisconsin undergraduate and graduate students who have contributed to the WIYN Open Cluster Study radial-velocity database.