Lithium in globular clusters: significant systematics. Atomic diffusion, the temperature scale, and pollution in NGC 6397

T. Nordlander (1) , A. J. Korn (1) , Olivier Richard (2) , K. Lind (3)

1 Department of Physics and Astronomy [Uppsala]
2 LUPM - Laboratoire Univers et Particules de Montpellier
3 MPA - Max-Planck-Institut für Astrophysik

We describe our latest investigation of stars in NGC 6397, as an update to Korn et al. There, effects of atomic diffusion were found to significantly affect surface abundances of lithium, as well as iron and magnesium. In this updated analysis, we have adopted a new, hotter, temperature scale. Additionally, we now analyze lithium in NLTE, have added chromium in NLTE to the analysis, and corrected magnesium abundances for effects of cluster-internal pollution. We determine abundances in six chemical elements. Significant evolutionary variations on the 3 sigma level are still identified in the iron abundances. Variations in all six elements match model predictions only if atomic diffusion processes are moderated by turbulent mixing of moderate efficiency. We infer an intial cluster lithium abundance abundance Li = 2.57 ± 0.10, which agrees with WMAP-calibrated BBN predictions, abundance Li = 2.71 ± 0.06.

Mots clés: diffusion; globular clusters: individual (NGC 6397); stars: abundances; stars: evolution; stars: fundamental parameters

Domaines: Astrophysique [astro-ph]

T. Nordlander, A. J. Korn, Olivier Richard, K. Lind. Lithium in globular clusters: significant systematics. Atomic diffusion, the temperature scale, and pollution in NGC 6397. Lithium in the Cosmos, 2012, Paris, France. ⟨hal-01993818⟩