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H. R. Jacobson, C. A. Pilachowski (Indiana University), E. D. Friel (National Science Foundation)
Evidence of atmospheric mixing has been observed in a variety of old (greater than Hyades age) open clusters. This evidence is manifested as enhancements in abundances of elements such as Na and Al in giants. Several studies have revealed open clusters of approximately solar [Fe/H] to have large Na and Al abundances relative to solar values. Such enhancements are unexpected, as mixing is not thought to occur in low-mass, metal-rich stars.
Here we present an analysis of Na and Al abundances of three intermediate- and old-aged open clusters: IC 4756 (~ 700 Myr), NGC 6939 (~ 1-2 Gyr), and NGC 7142 (~ 3-5 Gyr). The data were obtained with the Hydra multi-object spectrometer on the WIYN 3.5m operating in echelle mode (R~ 20,000). Multiple stars per cluster were analyzed and average cluster abundances of Na, Al, Fe and other elements were determined. Preliminary results are presented and compared to those of other open clusters of similar age. The elemental abundances of these clusters are also discussed in the context of the chemical evolution of the Galactic disk.
This research is supported by a National Science Foundation Graduate Research Fellowship.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.