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D. Yong, D. L. Lambert (University of Texas)
Our understanding of the evolution of the Galaxy is built in part on the interpretation of observed abundance ratios in stars of different metallicity. While elemental abundances may be easier to measure, different stellar sites and nucleosynthetic processes may be responsible for the production of the individual isotopes. Therefore, isotope ratios may provide a more detailed insight into the chemical evolution of the Galaxy. We conducted a search for cool metal-poor stars from which we measured Mg isotope ratios to study the chemical history of the Galaxy. Our data are in fair agreement with predictions that assume the isotopes are the product of massive stars. We find an intrinsic scatter at all metallicities which may be due to ejecta from AGB stars. To gauge non-LTE effects and inadequacies in the model atmospheres, we measured Mg isotope ratios in the Hyades open cluster. While the model atmospheres did not reproduce ionization equilibrium for Fe, the Mg isotope ratios were immune to these problems.
We have also used isotope ratios to study globular cluster chemical evolution. Every well studied Galactic globular cluster shows star-to-star differences in and correlations between the light elements. The mechanism responsible for these variations remains poorly understood. We measured Mg isotope ratios in the giant stars of globular cluster NGC 6752. Varying degrees of pollution by AGB stars of the same generation as the observed stars may explain our measured isotopic and elemental abundances.
This research was supported by the Robert A. Welch Foundation of Houston, Texas.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.