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First Stars III
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Poster
Title: HE 1327-2326 -- stellar parameters, atomic diffusion and lithium abundance Author(s): Andreas Korn Abstract: The recent discovery of systematic trends of elemental abundances with evolutionary stage in the globular cluster NGC 6397 (Korn et al. 2006, Nature 442, 657) has given support to the theoretical expectation that the abundances of elements in the atmospheres of unevolved halo stars are significantly affected by atomic diffusion (AD). This scenario offers the possibility to reconcile the lithium abundance measured in warm halo stars with the WMAP-based prediction of Big-Bang nucleoysnthesis. HE 1327, one of the two known hyper-metal-poor stars with [Fe/H] < -5, is in a near-turnoff state of evolution (Frebel et al. 2006) and seemingly has no lithium (log eps (Li) < 0.9). Based on various techniques we derive stellar parameters for this star. In particular, we derive a spectroscopic surface gravity based on the calcium ionization equilibrium in non-LTE (Mashonkina et al. 2007). We discuss how much the chemical abundances of HE 1327 are affected by AD and whether or not the apparent absence of lithium can be explained by stellar-structure models with AD.
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