PI: Bruce A. Twarog, University of Kansas, firstname.lastname@example.org
Address: Dept. of Physics & Astronomy, 1251 Wescoe Hall Dr., Lawrence, KS 66045, USA
CoI: Constantine Deliyannis, Indiana University
CoI: Barbara Anthony-Twarog, University of Kansas
Title: Constraining the Origin and Stellar Evolution of Li Using Giants in M92/NGC 2506, and Dwarfs in NGC 7789
Abstract: Three years ago we began a comprehensive program focused on the collection and analysis of high-dispersion spectra in the Li 6708 \AA\ region for 150-330 stars per cluster from the tip of the RGB to below the MS-turnoff in each of the open clusters NGC 2158, NGC 6819, and NGC 7789. We have combined intermediate-band photometry and spectroscopy of samples typically an order-of-magnitude larger than any previous open cluster study, to map the main sequence and post-main sequence evolution of Li with age and metallicity. Our success in these open clusters leads us to push the study limits to a moderately metal-poor cluster (NGC 2506, [Fe/H]=-0.4) and an exceptionally low-metallicity globular cluster (M92, [Fe/H]=-2.7) by probing the evolution of stars on their giant/subgiants branches. We will also push to dwarfs of NGC 7789 to compare with our results for NGC 6819. With ~ 150 stars to below the HB in M92, and ~100 stars to the turnoff in NGC 2506, we will (a) test the degree to which standard theory correctly predicts subgiant dilution, (b) search for Li-rich stars and empirically constrain the non-standard mixing mechanisms known to be at work on the RGB, and differentiate among proposed models, (c) test the impact of intracluster population inhomogeneities on the dispersion in Li, and (d) constrain the Big Bang Li abundance (Phase 2). With NGC 7789, we will constrain varied mechanisms proposed for the origin of the Li dip.
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