📝 SummarXiv

Abstract

We present 32 new spectroscopic-binary orbits from our extended radial-velocity (RV) survey of the old ($6.4 \pm 0.2$ Gyr) open cluster NGC 188. Using data from the WIYN Open Cluster Study (WOCS) and APOGEE-2, this work nearly doubles the temporal baseline of the previous RV study of NGC 188. We obtain orbital solutions within a stellar sample that spans a magnitude range of $10.8 \leq \mathrm{G} \leq 16.5 \; (0.9\mbox{-}1.2 \; {M_\odot})$. With revised membership determinations using Gaia DR3 proper-motions and parallaxes, we reassess the cluster binary frequency and period-eccentricity distribution, finding an incompleteness-corrected binary frequency of $33.1 \% \pm 3.8\%$ for periods less than $10^4$ days. We also find a tidal-circularization period of $14.4^{+0.14}_{-0.11}$ days. We find evidence that giants are deficient in short-period orbits, and suggest that the missing giants may have undergone mass transfer and in part formed the population of blue straggler stars and blue lurkers. Among the binaries of note, we highlight WOCS 3953 and WOCS 4945, long-period candidate mass-transfer systems that exhibit possible UV excess.