WIYN Open Cluster Study. LXXXII. Radial-velocity Measurements and Spectroscopic Binary Orbits in the Open Cluster NGC 7789

We present an extensive time-series radial-velocity (RV) survey of stars in the rich open cluster NGC 7789 (1.6 Gyr, [Fe/H] = +0.02). The stellar sample lies within an 18′ circular radius from the cluster center (10 pc in projection, or about 2 core radii), and includes giants, red clump stars, blue stragglers, red stragglers, sub-subgiants, and main-sequence stars down to 1 mag below the turnoff. Our survey began in 2005 and comprises more than 9000 RV measurements from the Hydra Multi-Object Spectrograph on the WIYN 3.5 m telescope. We identify 624 likely cluster members and present the orbital solutions for 81 cluster binary stars with periods between 1.45 and 4200 days. From the main-sequence binary solutions we fit a circularization period of ${7.2}_{-1.1}^{+0.6}$ days. We calculate an incompleteness-corrected main-sequence binary frequency of 31% ± 4% for binaries with periods less than 10⁴ days, similar to other WIYN Open Cluster Survey (WOCS) open clusters of all ages. We detect a blue straggler binary frequency of 33% ± 17%, consistent with the similarly aged open cluster NGC 6819. We also find one secure, rapidly rotating sub-subgiant and one red straggler candidate in our sample.