AAS 207th Meeting, 8-12 January 2006
Session 71 (WIYN) Open Clusters and Associations
Poster, Tuesday, 9:20am-6:30pm, January 10, 2006, Exhibit Hall

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[71.03] WIYN Open Cluster Study: Tidal Circularization in NGC 6819

S. Yelda (U. Michigan), R. D. Mathieu, S. Meibom (U. Wisconsin)

The orbital parameters of close binary systems are constantly changing due to the effects of tidal circularization. We measured this effect in the intermediate-age (~2.5 Gyr) open cluster NGC 6819 by determining the tidal circularization period as defined by Meibom & Mathieu (2005, ApJ, 620, 970). This is the longest period at which a typical binary has evolved to an eccentricity consistent with zero in the age of the population. The distribution of orbital eccentricity versus orbital period for 39 main-sequence spectroscopic binaries in the cluster shows a tidal circularization period of ~ 7.5 days. When compared to other coeval populations, we find that this result is consistent with the overall trend of increasing tidal circularization period with population age. These findings derive from 6410 radial-velocity measurements of 1356 stars with 12.5 < V < 16.5 (Hole et al. 2005, AJ, submitted) using the WIYN Hydra Multi-Object Spectrograph. Typical velocity measurement precisions are ~0.3 km/sec. SY was supported by REU NSF grant AST-0453442. RDM and SM are supported by NSF grant AST-0406615.

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