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Title:
WIYN Open Cluster Study. XXIV. Stellar Radial-Velocity Measurements in NGC 6819
Authors:
Hole, K. Tabetha; Geller, Aaron M.; Mathieu, Robert D.; Platais, Imants; Meibom, Søren; Latham, David W.
Affiliation:
AA(Astronomy Department, University of Wisconsin-Madison, 475 N Charter St, Madison, WI 53706, USA ; Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation.; ), AB(Astronomy Department, University of Wisconsin-Madison, 475 N Charter St, Madison, WI 53706, USA ; Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation.; ), AC(Astronomy Department, University of Wisconsin-Madison, 475 N Charter St, Madison, WI 53706, USA ; Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation.; ), AD(Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA ), AE(Astronomy Department, University of Wisconsin-Madison, 475 N Charter St, Madison, WI 53706, USA ; Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA ; Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation.; ), AF(Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA )
Publication:
The Astronomical Journal, Volume 138, Issue 1, pp. 159-168 (2009). (AJ Homepage)
Publication Date:
07/2009
Origin:
IOP
AJ Keywords:
open clusters and associations: individual: NGC 6819, techniques: radial velocities
DOI:
10.1088/0004-6256/138/1/159
Bibliographic Code:
2009AJ....138..159H

Abstract

We present the current results from our ongoing radial-velocity (RV) survey of the intermediate-age (2.4 Gyr) open cluster NGC 6819. Using both newly observed and other available photometry and astrometry, we define a primary target sample of 1454 stars that includes main-sequence, subgiant, giant, and blue straggler stars, spanning a magnitude range of 11 <=V<= 16.5 and an approximate mass range of 1.1-1.6 M sun. Our sample covers a 23 arcminute (13 pc) square field of view centered on the cluster. We have measured 6571 radial velocities for an unbiased sample of 1207 stars in the direction of the open cluster NGC 6819, with a single-measurement precision of 0.4 km s-1 for most narrow-lined stars. We use our RV data to calculate membership probabilities for stars with >=3 measurements, providing the first comprehensive membership study of the cluster core that includes stars from the giant branch through the upper main sequence. We identify 480 cluster members. Additionally, we identify velocity-variable systems, all of which are likely hard binaries that dynamically power the cluster. Using our single cluster members, we find a cluster average RV of 2.34 ± 0.05 km s-1. We use our kinematic cluster members to construct a cleaned color-magnitude diagram from which we identify rich giant, subgiant, and blue straggler populations and a well defined red clump. The cluster displays a morphology near the cluster turnoff clearly indicative of core convective overshoot. Finally, we discuss a few stars of note, one of which is a short-period red-clump binary that we suggest may be the product of a dynamical encounter.
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