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Session 85 - Cosmology: Observations.
Display session, Friday, January 09
The best source from which to discern the value of primordial Li is main--sequence stars in globular clusters. By observing turn--off stars with the same temperature in a globular cluster, we can remove age, metallicity, mass, luminosity, and temperature from the parameter space. We can examine the effects of age and metallicity by observing stars in more than one globular cluster.
We present Keck I HIRES observations of Li in turn--off stars in three globular clusters, M 92, M 13, and M 71. These clusters range in age from 12 to 16 Gyr and in metallicity from [Fe/H] = --0.6 to --2.25. The spectra have a resolution of 48,000 and signal--to--noise ratios of 30--40. The integration times were up to five hours for each 18th magnitude star at Keck I. We have found a dispersion in the amount of Li -- of more than a factor of three -- in otherwise identical stars in each of the clusters. A Li dispersion indicates that it is stellar processing, not galactic processing, that affects the Li abundance since galactic processing ought to affect the all the stars in a given cluster the same way. We suggest that the dispersion is due to different amounts of initial angular momentum in the individual stars which results in different amounts of Li depletion as the stars spin down. Those with the highest angular momentum would have spun down the most and thus have the lowest Li at present. The highest Li abundances are log N(Li) = 2.5 which gives a lower limit for primordial Li. The implications for the conditions in the Big Bang will be discussed.
Program listing for Friday