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We analyse high-resolution archival UVES data of turnoff and subgiant stars in the nearby globular cluster NGC6397 ([Fe/H]≈−2). Balmer-profile analyses are performed to derive reddening-free effective temperatures. Due to the limited S/N and uncertainties related to blaze removal, we find the data quality insufficient to exclude the existence of gravitational settling. If the newly derived effective temperatures are taken as a basis for an abundance analysis, the photospheric iron (Fe ii) abundance in the turnoff stars is 0.11 dex lower than in the (well-mixed) subgiants.

Red giant stars, both in the field and in globular clusters, present abundance anomalies that can not be explained by standard stellar evolution models. Some of these peculiarities, such as the decline of C/C, and that of Li and C surface abundances for stars more luminous than the , clearly point towards the existence of extra-mixing processes at play inside the stars, the nature of which remains unclear. Rotation has often been invoked as a possible source for mixing inside Red Giant Branch (RGB) stars ([8],[1],[2]). In this framework, we present the first fully consistent computations of rotating low mass and low metallicity stars from the Zero Age Main Sequence (ZAMS) to the upper RGB.

We present preliminary results of 3D hydrodynamical simulations of surface convection in red giants stars. We investigate the main differences between static 1D and 3D time-dependent model stellar atmospheres of red giants for a range of metallicities between solar and [Fe/H] = −3 focusing in particular on the impact of 3D spectral line formation on the derivation of stellar abundances.

Rotation plays a major role in massive star evolution. Rotation produces a significant mixing and enhances the mass loss. All model outputs are influenced. We show how the chemical yields are modified by rotation. Below 30 ⊙, mixing increases the yields of the α–elements and above 30 ⊙ rotational mass loss dominates and enhances the yield in helium. Primary N is produced at very low metallicities.

The astrophysical origin of the rapid neutron-capture (-process) species has been a long-standing mystery. Even the most promising, “neutrino wind” scenario, encounters some difficulties [5]. Recent chemical evolution studies imply the dominant source of -process elements to be the low-mass end of the supernova mass range, such as stars of 8–10⊙ [1,2]. The purpose of this study is to investigate conditions necessary for the production of -process nuclei obtained in purely hydrodynamical models of prompt explosions of collapsing O-Ne-Mg cores, and to explore some of the consequences if those conditions are met (see [7,8] for more detail).

Neutron captures in massive stars are mostly driven by the Ne(α,n)Mg reaction. A large abundance of Ne results from the previous conversion of original CNO nuclei into N during H burning followed by N(,)F()O(,)Ne during the early phases of He burning. The β-decay by F makes the neutron excess that allows the neutron source for the s process. A number of works in the past followed the s process during core He burning, where the average neutron density barely achieves 10 n/cm ([2] and references therein).

The recent discovery of a new population of stars exhibiting unusual elemental abundance patterns characterized by enhanced Ti to Ga elements and low α-elements suggests the contribution of a new class of supernovae, probably a kind of Type Ia supernovae associated with close binary evolution. The role of these supernovae in chemical evolution is negligible in normal galaxies that undergo moderate star formation such as our own. Thus, while the frequency of occurrence would be too low to detect in low-redshift galaxies, it may represent a prominent population in high-redshift objects such as early epoch massive elliptical galaxies and QSOs. The chemical contributor of this proposed type of supernovae in combination with recognized supernovae is compatible with the recent observational features in the distant universe.

The interest of the astrophysical community on the evolution of the intermediate mass stars (IMS) raised in the last decades, as they have been suggested as possible responsible of the chemical anomalies which are observed in Giant and TO stars within Globular Clusters (see e.g. Gratton et al. 2004).

The relic abundances of the light elements synthesized during the first few minutes of the evolution of the Universe provide unique probes of cosmology and the building blocks for stellar and galactic chemical evolution, while also enabling constraints on the baryon (nucleon) density and on models of particle physics beyond the standard model. Recent WMAP analyses of the CBR temperature fluctuation spectrum, combined with other, relevant, observational data, has yielded very tight constraints on the baryon density, permitting a detailed, quantitative confrontation of the predictions of Big Bang Nucleosynthesis with the post-BBN abundances inferred from observational data. The current status of this comparison is presented, with an emphasis on the challenges to astronomy, astrophysics, particle physics, and cosmology it identifies.

We recall the emergence of the “He problem”, its currently accepted solution, and we summarize the presently available constraints on models of stellar nucleosynthesis and studies of Galactic chemical evolution from observations of the He isotopic ratio in the Galaxy.