WIYN OPEN CLUSTER STUDY. XXIV. STELLAR RADIAL-VELOCITY MEASUREMENTS IN NGC 6819

Abstract

We present the current results from our ongoing radial-velocity survey of the\nintermediate-age (2.4 Gyr) open cluster NGC 6819. Using both newly observed and\nother available photometry and astrometry we define a primary target sample of\n1454 stars that includes main-sequence, subgiant, giant, and blue straggler\nstars, spanning a magnitude range of 11<=V<=16.5 and an approximate mass range\nof 1.1 to 1.6 Msun. Our sample covers a 23 arcminute (13 pc) square field of\nview centered on the cluster. We have measured 6571 radial velocities for an\nunbiased sample of 1207 stars in the direction of the open cluster NGC 6819,\nwith a single-measurement precision of 0.4 km/s for most narrow-lined stars. We\nuse our radial-velocity data to calculate membership probabilities for stars\nwith >= 3 measurements, providing the first comprehensive membership study of\nthe cluster core that includes stars from the giant branch through the upper\nmain sequence. We identify 480 cluster members. Additionally, we identify\nvelocity-variable systems, all of which are likely hard binaries that\ndynamically power the cluster. Using our single cluster members, we find a\ncluster average radial velocity of 2.34 +/- 0.05 km/s . We use our kinematic\ncluster members to construct a cleaned color- magnitude diagram from which we\nidentify rich giant, subgiant, and blue straggler populations and a\nwell-defined red clump. The cluster displays a morphology near the cluster\nturnoff clearly indicative of core convective overshoot. Finally, we discuss a\nfew stars of note, one of which is a short-period red-clump binary that we\nsuggest may be the product of a dynamical encounter.\n