The open cluster NGC 6791 has been the focus of much recent study due to its intriguing combination of old age and high metallicity ( \sim 8 Gyr , [ Fe / H ] = + 0.30 ) , as well as its location within the Kepler field .
As part of the WIYN Open Cluster Study , we present precise ( \sigma = 0.38 km s ^ { -1 } ) radial velocities for proper-motion candidate members of NGC 6791 from Platais et al .
Our survey , extending down to g ^ { \prime } \sim 16.8 , is comprised of the evolved cluster population , including blue stragglers , giants , and horizontal branch stars .
Of the 280 proper-motion-selected stars above our magnitude limit , 93 % have at least one radial-velocity measurement and 79 % have three measurements over the course of at least 200 days , sufficient for secure radial-velocity-determined membership of non-velocity-variable stars .
The Platais et al .
proper-motion catalog includes twelve anomalous horizontal branch candidates blueward of the red clump , of which we find only four to be cluster members .
Three fall slightly blueward of the red clump and the fourth is consistent with being a blue straggler .
The cleaned color-magnitude diagram shows a richly populated red giant branch and a blue straggler population .
Half of the blue stragglers are in binaries .
From our radial-velocity measurement distribution we find the cluster ’ s radial-velocity dispersion to be \sigma _ { c } = 0.62 \pm 0.10 km s ^ { -1 } .
This corresponds to a dynamical mass of \sim 4600 M _ { \odot } .