AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 5. Star Formation in Dwarfs and Irregulars
Display, Monday, May 31, 1999, 9:20am-6:30pm, Southwest Exhibit Hall

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[5.03] The Metallicity Distribution of Red Giants in the Large Magellanic Cloud

A.A. Cole (University of Wisconsin-Madison), T.A. Smecker-Hane (University of California, Irvine), J.S. Gallagher (University of Wisconsin-Madison)

The ``dark ages'' for knowledge of the Large Magellanic Cloud's (LMC's) stellar populations extend from 3--10 Gyr. A particularly large gap exists in our characterization of the LMC age-metallicity relation, because the most obvious tracers of such a relation, populous star clusters, show a bimodal distribution in both age and metallicity that does not appear sufficient to trace the evolution of the field star populations during this period.

We used the Blanco 4-meter telescope at CTIO with the R-C spectrograph to obtain spectra at the \lambda \approx 8500 Å\ Ca {\small II} triplet for two dozen red giants in a field that we have observed with WFPC2. These data have allowed us to directly measure metallicities for a subsample of the stars in our color-magnitude diagrams, alleviating the age-metallicity degeneracy. The detailed star-formation and chemical abundance history obtained from our combined datasets allows us to discriminate between competing models that have been proposed for the history of the LMC.

The disparity in size between photometric and spectroscopic datasets has led us to explore the use of photometric abundance indicators. We have obtained Strömgren photometry, using the CTIO 1.5-meter telescope, for these same fields in the LMC. Our aim is to tie this less precise but more efficient abundance estimator to the Ca {\small II} triplet metallicity scale, and obtain direct metallicity information for tens of thousands of stars. The abundance distribution function thus derived will be an important constraint on models of the LMC's star-formation history.

Travel support for this program has been provided to A.A.C. by the Cerro Tololo Inter-American Observatory (CTIO).

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