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K.T. Hole, R.D. Mathieu, S. Meibom (University of Wisconsin - Madison)
We present results of a radial-velocity study of the 2.5 Gyr old open cluster NGC 6819. We have 5140 radial velocity measurements of 1140 stars, obtained over the course of approximately 5 years with the WIYN Multiple-Object Spectrograph. The standard deviation of the measurements for a single (formally, non-variable) star is 0.5 km/s. We have measured velocities for the brighter evolved stars and main sequence stars to V=16.5. We are very nearly complete for stars above the main sequence and approximately 50% complete on the main sequence.
We find the cluster mean velocity to be 2.3 km/s with an observed dispersion of 1.5 km/s; we anticipate that the true cluster velocity dispersion is smaller. We discuss the distribution of velocities in the cluster field of view, and related issues of membership selection. We present a CMD of all data, and a "clean" CMD of cluster member stars.
Our later measurements have emphasized velocity-variable stars, and we have orbital solutions for 35 binaries. Our solutions to the orbits of these binaries will allow us to investigate the evolution of dynamical properties of the systems. Of particular interest is the relationship of eccentricity to period, which indicates the tidal circularization cutoff for the cluster.
This research was funded in part by NSF AST 9731302, Wisconsin Space Grant Consortium, and Oberlin College.
The author(s) of this abstract have provided an email address for comments about the abstract: kth@astro.wisc.edu
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.