Collaborative Research: Fundamental Properties of Local Subdwarfs

Ohio State University Research Foundation -Do Not Use, Columbus OH

Investigators

Abstract

AST 0205789 Terndrup Many outstanding issues concerning the formation and evolution of the Milky Way require improved knowledge of the kinematics and chemical enrichment patterns of local metal-poor subdwarfs in the Galaxy's halo and thick disk, and how these compare to globular cluster stars. Even after several recent efforts, current samples do not adequately cover the range of metallicities and kinematics seen in globular clusters, while observations of local metal-poor giants give tantalizing evidence of significant differences between local halo stars and those in globular clusters of the same metallicity. This project will improve the observational situation by obtaining accurate and self-consistent measures of temperature, reddening, and composition for a critically selected sample of approximately 150 subdwarfs identified in recent surveys for metal-poor stars. There will also be new theoretical efforts to explore the dependence of the main-sequence luminosity on detailed stellar chemical composition and on often-neglected physics such as helium diffusion and rotation. This project will also yield valuable information on the kinematics and star formation history of the halo and the metal-poor tail of the thick disk, identify samples of subdwarfs that are well matched in abundance patterns and kinematics to globular cluster stars, and improve the temperature and abundance scales of globular cluster main sequences for comparison to spectroscopic determinations on the giant branch. There will also be a systematic study of the relative and absolute ages of globular clusters, with a focus on reducing the errors in the theoretical plane. Importantly, this project will enable the community to take full advantage of the future FAME and SIM satellite missions, which will measure accurate parallaxes for the subdwarfs in the sample and thereby yield the absolute calibration of the main-sequence luminosity for globular clusters and hence their distances. Current distance estimates are only good to 10 - 15%, resulting in age errors of about 30%, insufficient to reliably explore the age spread in the globular cluster system or even set lower limits to the age of the Universe by comparison with the predictions of stellar evolution theory.