AAS 207th Meeting, 8-12 January 2006
Session 91 Star Clusters Large and Small
Oral, Tuesday, 10:00-11:30am, January 10, 2006, Balcony A

## [91.07] Chemical Abundances of Solar-Type Dwarfs in Open Clusters

S.C. Schuler (Clemson Univ.)

Open clusters present homogeneous samples of stars that are of the same age, distance, and initial chemical composition, making open clusters valuable observational targets for studies of stellar evolution, stellar structure, exoplanetary systems, and Galactic chemical evolution. I present an overview of my graduate dissertation research on LTE abundances of solar-type dwarfs (4200 \lesssim T\rm eff \lesssim 6400 \; \rm{K}) in the open clusters Pleiades, M34, and Hyades, as well as in the Ursa Major moving group. For the dwarfs of intermediate T\rm eff (5500 \lesssim T\rm eff \lesssim 6100 \; \rm{K}), intracluster metal abundances are in good agreement. Conversely, we have identified excitation/ionization-related abundance anomalies among the cool dwarfs (T\rm eff \leq 5500 \; \rm{K}) of all three clusters and UMa; for example, O abundances derived from the high-excitation, near-IR \ion{O}{1} triplet show a dramatic increase with decreasing T\rm eff, a behavior that is not predicted by current non-LTE calculations. Intercluster comparisons are suggestive of an age-related diminution of the \ion{O}{1} triplet abundance trend, and possible causes of these observed abundance anomalies, i.e., chromospheric activity, surface inhomogeneities, etc., are explored. Using multi-component toy model'' stellar atmospheres, we demonstrate that the \ion{O}{1} triplet abundance trend may be due to inhomogeneous temperature structure, possibly resulting from spots or plages, in the photospheres of cool open cluster dwarfs.

I gratefully acknowledge the following agencies that have provided support during this research: NSF (through grants AST 00-86576 and AST 02-39518 to Prof. J.R. King), South Carolina Space Grant Consortium (through the Graduate Student Research Fellowship program), and the Charles Curry Foundation (through a generous grant to Clemson University).