The AMS-02 experiment is a large acceptance magnetic spectrometer which will operate on the International Space Station for more than 3 years. This will allow to perform high statistics studies of cosmic rays in space and the accurate determination of secondary-to-primary ratios such as B/C, and the ratio $^{10}$Be/$^{9}$B, thus allowing to discriminate among the possible propagation models and to infer other clues about the light elements production.

Effective temperatures of 30 turnoff stars with $-3.2 {<}$[Fe/H]${<}{-}1.5$ have been derived from the profiles of Balmer lines in high S/N, VLT/UVES spectra. While the systematic error of $T_{\rm eff}$ may be of the order of 100K, the differential values of $T_{\rm eff}$ are determined with a one-sigma precision of ${\sim}25$K. These precise $T_{\rm eff}$ values are used in a study of the slope and dispersion of the Li abundance as a function of [Fe/H]. A small, but significant cosmic dispersion in $A$(Li) appears to be present exemplified by the two very metal-poor stars G64-12 and G64-37.

The rare light elements — Li, Be, and B — have a unique and highly coupled history in the Universe. A coordinated analysis of their abundances in very low metallicity stars can help us understand the inner workings of stars and can constrain models of Galactic chemical evolution. We measure the Be abundances of nine stars and the Li isotopic ratio of ten stars. We find three stars with interesting Be abundances and three stars with detectable $^6$Li.

We have computed updated models of population II stars on the Spite plateau. We focus here on the light elements abundance predictions when the new tachocline mixing process is accounted for.

The international Project “Lithium in magnetic CP stars” has been put into operation using telescopes of the Crimean Astrophysical Observatory (2.6-m reflector ZTSH), European Southern Observatory (1.4-m CAT, 1.52-m with FEROS), Mount Stromlo Observatory (74-inch), Nordic Optical Telescope Scientific Association (2.4-m with SOFIN), Special Astrophysical Observatory of the Russian Academy of Sciences (6-m BTA). Here we present an historical report of the different scientific results of this project since its beginning in 1996.

We report on results of VLT/FLAMES observations of the very old cluster Cr 261. We compare the results with those of other clusters older than the Hyades.

A deformation of the interface between convectively stable, unstable layers in a star can lead to intensified mixing of the elements. Our three-dimensional simulations show that under a condition of deformability of the interface, a coupled long-lived system of large-scale flows, penetrative convection is established. This effect can explain lithium depletion in the solar atmosphere

We constrain energy spectra of supernova neutrinos using the $\nu$-process light element synthesis in supernovae and the $^{11}$B abundance during Galactic chemical evolution. We calculate supernova nucleosynthesis due to the $\nu$-process assuming that neutrino energy spectra are Fermi-Dirac distributions with zero chemical potential. We investigate the dependence of the $^{11}$B yield on the total neutrino energy and the temperature of $\nu_{\mu,\tau}$ and $\bar{\nu}_{\mu,\tau}$. From the obtained yields and the contribution to the $^{11}$B yield from supernovae constrained by observed abundances and Galactic chemical evolution models, we find an acceptable range of the temperature of $\nu_{\mu,\tau}$ and $\bar{\nu}_{\mu,\tau}$ of 4.8 MeV to 6.6 MeV.

How and when did the first generation of stars form at the end of the cosmic dark ages? Quite generically, within variants of the cold dark matter model of cosmological structure formation, the first sources of light are expected to form in $\sim 10^{6} M_{\odot}$ dark matter potential wells at redshifts $z\geq 20$. I discuss the physical processes that govern the formation of the first stars. These so-called Population III stars are predicted to be predominantly very massive, and to have contributed significantly to the early reionization of the intergalactic medium. Such an early reionization epoch is inferred from the recent measurement of the Thomson optical depth by the WMAP satellite. I address the importance of heavy elements in bringing about the transition from an early star formation mode dominated by massive stars, to the familiar mode dominated by low mass stars, at later times, and present possible observational probes. This transition could have been gradual, giving rise to an intermediate-mass population of still virtually metal-free stars (“Population II.5”). These stars could have given rise to the peculiar class of black-hole forming supernovae inferred from the abundance pattern of extremely iron-poor stars.

Motivated by the WMAP results indicating an early epoch of reionization, we consider alternative cosmic star formation models which are capable of reionizing the early intergalactic medium. We develop models which include an early burst of massive stars (with several possible mass ranges) combined with standard star formation, in the framework of the hierarchical scenario of structure formation. We compute as a function of redshift the stellar ionizing flux of photons, the supernova rates and the chemical evolution, both in the intergalactic medium and in the interstellar medium of forming galaxies. We apply constraints from the cosmic observed star formation rate and the observed abundances in the Lyman $\alpha$ forest and in Damped Lyman $\alpha$ clouds in conjunction with the ability of the models to produce the required degree of reionization.

We discuss the effects of very massive Population III stars on the chemical evolution of the Milky Way, elliptical galaxies and the intergalactic medium (IGM) at high reshift. It is shown that the effects produced by Pop III stars on the early evolution of the most common chemical abundances (C, N, O, $\alpha$-elements, Fe) are negligible if these stars formed only for a very short period of time, corresponding to the suggested threshold metallicity ($Z_{thr} \sim 10^{-4}Z_{\odot}$). For a higher threshold metallicity and therefore a longer period of time, the predicted results are at variance with observations. It is also concluded that the IGM at high redshift ($z=5.0$) cannot have been enriched only by very massive Pop III stars, but that the contribution of lower mass stars is necessary. The same conclusion holds for DLA systems at high redshift.

Rotating massive stars at $Z=10^{-8}$ and $10^{-5}$ lose a great part of their initial mass through stellar winds. The chemical composition of the rotationally enhanced winds of very low $Z$ stars is very peculiar. The winds show large CNO enhancements by factors of $10^3$ to $10^7$, together with large excesses of $^{13}$C and $^{17}$O and moderate amounts of Na and Al. The excesses of primary N are particularly striking. When these ejecta from the rotationally enhanced winds are diluted with the supernova ejecta from the corresponding CO cores, we find [C/Fe], [N/Fe],[O/Fe] abundance ratios very similar to those observed in the C–rich extremely metal poor stars (CEMP). We show that rotating AGB stars and rotating massive stars have about the same effects on the CNO enhancements. Abundances of s-process elements and the $^{12}$C/$^{13}$C ratio could help us to distinguish between contributions from AGB and massive stars. On the whole, we emphasize the dominant effects of rotation for the chemical yields of extremely metal poor stars.

Theoretical estimates of nucleosynthesis yields are widely used to infer the meaning of abundance trends, and to predict behavior of abundances in the first stars. We show that the standard prescriptions are incomplete, and illustrate some simple improvements. We consider the effects of internal gravity waves (induced in radiative regions by convective zones) on the evolution of slowly rotating (nonrotating) stars. We demonstrate that such modifications to the standard evolutionary algorithms give better agreement with observation. They imply new phenomena: interations between carbon and oxygen burning shells, detached flames in convective layers, and intermittency, for example. We argue that such hydrodynamic behavior must be part of realistic stellar evolution. Some preliminary results for the Sun and Sirius are discussed.

We show that rotation plays a major role for very low metallicity stars, even if the distribution of angular velocities $\Omega$ with respect to critical values is the same as at solar $Z$. The internal gradients of $\Omega$ are much larger at lower metallicity $Z$, which enhance internal mixing and give rise to N-enrichments. Low $Z$ stars easily reach break–up during MS evolution and lose mass. They also lose mass as red giants or supergiants due to their surface enrichments in heavy elements. The winds of low $Z$ stars make peculiar contributions to the chemical yields. We suggest that the helium rich blue Main Sequence (bMS) of $\omega$ Centauri bears the signature of such enrichments by the stellar winds of rotating stars in the first stellar generations.

In order to study the effects of fast rotation on primordial stars, we present the evolution and the chemical yields of zero metallicity models with masses between 15 to 200 M[odot ].

We study dynamical aspects of circumstellar environment around massive first stars. We show that the stellar winds from stationary massive first generation (Population III) stars driven either by the line or continuum transitions are unlikely. Massive first stars are also unable to expel any element or isotope with a possible exception of $_1^1$H. H-He stars with Eddington parameter $\Gamma\gtrsim$0.859 may have pure-hydrogen wind with mass-loss rates of order $10^{-14}\text{M}_\odot\text{year}^{-1}$. Finally, we show that hydrogen and helium lines could be important for shutting off the initial accretion onto first stars and may influence the initial mass function of first stars.

We calculate evolution, explosion and nucleosynthesis of 1000$M_{\odot}$ stars. Even such massive stars may explode at the end of their lives if they rotate. We use a 2 dimensional hydrodynamical code to take aspherisity by the effect of rotation into account. Our results show that (1) abundance pattern of ejected matter by explosion is consistent with observational data of intracluster medium gas and M82 hot gas, (2) such massive stars can supply more efficient UV photons to re-ionize HI, HeI and HeII than ordinary massive stars (less than 100 solar-masses) and (3) final black hole mass is 500 solar-mass, which is consistent of the mass scale of intermediate-mass black hole (IHBH) found in M82.

We present results from an Eulerian adaptive mesh refinement simulation demonstrating the formation of a primordial star within an HII region produced by an earlier massive star. Despite the higher temperatures of the ionized gas, this second star formed within 23 million years of its neighbor's death. The enhanced electron fraction within the HII region catalyzes rapid molecular hydrogen formation, leading to enhanced cooling in the preprocessed halo. This “second generation” primordial protostar has a much lower accretion rate than its predecessor, due in part to the higher angular momentum of the halo in which it forms. This situation may allow binaries or multiple systems of low-mass stars to form. The result discussed here is described in more detail in O'Shea et al. (2005).

We report on the distribution of metallicities, [Fe/H], for very metal-poor stars in the halo of the Galaxy. Although the primary information on the nature of the Metallicity Distribution Function (MDF) is obtained from the two major recent surveys for metal-poor stars, the HK survey of Beers and collaborators, and the Hamburg/ESO Survey of Christlieb and collaborators, we also discuss the MDF derived from the publicly available database of stellar spectra and photometry contained in the third data release of the Sloan Digital Sky Survey (SDSS DR-3). Even though the SDSS was not originally planned as a stellar survey, significant numbers of stars have been observed to date – DR-3 contains spectroscopy for over 70,000 stars, at least half of which are suitable for abundance determinations. There are as many very metal-poor ([Fe/H] $< -2.0$) stars in DR-3 as have been obtained from all previous survey efforts combined. We also discuss prospects for significant expansion of the list of metal-poor stars to be obtained from the recently funded extension of the SDSS, which includes the project SEGUE: Sloan Extension for Galactic Understanding and Evolution.

As part of a study of the detailed abundance patterns in extremely metal-poor stars, we have compared our samples of giants and dwarfs with two samples of dwarfs measured by different teams. For most elements the abundances are in good agreement, but for C, Na, and Al we show that the atmospheric abundances are different in dwarfs and in giants. For C the difference could be explained by “atmospheric effects” or by the influence of the first dredge-up, but for Na and Al deep mixing inside the stars must be invoked. Until now, such deep mixing has not been observed in metal-poor field stars. An excess scatter in [Mg/Fe] in giants remains unexplained.