PI: Barbara Anthony-Twarog, University of Kansas, email@example.com
Address: Physics Department, 1251 Wescoe Hall Dr., Lawrence, KS 66045, U.S.A.
CoI: Bruce Twarog, University of Kansas
CoI: Con Deliyannis, Indiana University
Title: Constraining the Evolution and Origin of Li Via Open Clusters: NGC 2204 and NGC 188
Abstract: Building on successful surveys in NGC 3680 and NGC 6253, several years ago we undertook to obtain Li abundances for statistically significant samples of (250 - 350) stars in each of the open clusters NGC 2158, 6811, 6819 and 7789. We have combined intermediate-band photometry with high-dispersion spectroscopy to map the main-sequence (MS) and post-MS surface evolution of Li for clusters of varying age and metallicity. In addition to establishing the [Fe/H] dependence of star mass at the center of the MS Li-dip, we have found several Li-rich first- ascent giants in NGC 6819 and 2158 and have verified the coincidence between the warm-side of the MS Li-dip and a MS gap in NGC 7789, suggesting a link between convection-induced gaps and the development of the dip. The current proposal addresses the only remaining weaknesses in our sample: metal-deficient and/or very old clusters. We hope to obtain complete observations of NGC 2204, a cluster in the 1.5-2.0 Gyr range with [Fe/H] below -0.30 and the iconic NGC 188 at 7 Gyr. We will continue to survey for Li-rich giants, particularly below the red clump level. We will also probe the connection (if any) between the cluster's original Li abundance, exemplified by the unmodified Li abundance of stars above the MS dip, and cluster [Fe/H], as a way to gain insight into galactic Li evolution and cosmology.
National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360