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The p-p chain is the series of nuclear reactions converting four protons to one He nucleus and releasing an energy of about 6.6 MeV/nucleon or 5 10 erg/gr. This provides the main source of energy for Main sequence ▶ stars of less than 1.3 M. while in more massive stars the ▶CNO cycle dominates. The first reaction of the series (p + p ! D + e + ne + 0.42 MeV) involves a slow, weak interaction (the conversion of a proton into a neutron), which is responsible for the long lifetimes (>10 Gyr) of the Sun and other low mass stars.

Gamma-ray line fluxes from the deexcitation of nuclei in accretion disks around galactic black holes are evaluated in the framework of the ADAF model. It is argued that previous evaluations have overestimated those fluxes and that, even under very optimistic assumptions, only the Sgr A ∗ black hole in the Galactic Center could be marginally detectable by INTEGRAL.

Dust depletion plays a key role in understanding the nature of Damped Lyman or systems (DLAs). In this paper we point out a previously unnoticed anticorrelation between the observed abundance ratio [X/Zn] (where Zn is assumed to be undepleted and X stands for the refractories Fe, Cr and Ni) and metal column density ([Zn/H] + log(N-HI)) in DLAs. We suggest that this trend is an unambiguous sign of dust depletion, since metal column density is a measure of the amount of dust along the line of sight. Assuming that DLAs are (proto-) galactic disks and using detailed chemical evolution models with metallicity dependent yields we study chemical evolution and dust depletion patterns for ct and iron-peak elements in DLAs. When observational constraints on the metal column density of DLAs are taken into account las suggested in Boisse et al. 1998) we find that our models reproduce fairly well the observed mild redshift evolution of the abundances of 8 elements (Al, Si, S, Cr, Mn, Fe, Zn and Ni) as well as the observed scatter at a given redshift. By considering the aforementioned dependence of abundance ratios on metal column density, we further explore the general dust depletion pattern in DLAs, comparing to our model results and to a solar reference pattern. We find that for low metal column densities (no depletion), our models compare fairly well to the data, while a solar pattern has difficulties with Mn. At high metal column densities (amount of depletion similar to0.5 dex), the solar pattern describes the data quite well, while our models have difficulties with S. We suggest that further measurements of those key elements, i.e. Zn, S and Mn, will help us to gain more insight into the nature of DLAs. The presently uncertain nucleosynthesis of Zn in massive stars Ion which a large part of these conclusions is based) should be carefully scrutinised.

We review the yields of intermediate mass elements (from C to Zn) from massive stars and their associated uncertainties, in the light of recent theoretical results. We consider the role of those yields for our understanding of the chemical evolution of the solar neighbourhood and of the halo of our Galaxy. Current yields reproduce in a satisfactory way the solar system composition, but several problems remain concerning abundance ratios in halo stars., Comment: 16 pages, 4 figures. Invited Review, to appear in ``The Interplay between Massive Stars and the ISM'', Guest Eds. D. Schaerer and R. G. Delgado, New Astronomy Reviews

Stellar reaction rates for proton captures on the nuclei 27Si, 31S, 35Ar, and 39Ca are estimated from the most recent nuclear structure information available. Reliable mirror-state correspondences are found by using the isobaric multiplet mass equation. An improved method for calculating proton partial widths is applied. Systematic comparisons of excitation energies, spectroscopic factors, proton partial widths, and γ-ray partial widths for states of the same isospin multiplet are presented. Stellar reaction-rate uncertainties are deduced, and our reaction rates are compared to previous estimates. Reaction network calculations are performed to investigate implications of the new reaction rates for nucleosynthesis in novae and X-ray bursts. Our recommended reaction rates are varied within their assigned uncertainties, and we find only minor effects on the nuclear energy generation and the final abundances after the outbursts. Thus, contrary to previous claims, we find no compelling reason for measuring the proton capture reactions on 27Si, 31S, 35Ar, and 39Ca by using radioactive ion beams.

A brief review is presented of our current understanding of the chemical evolution of the Milky Way and, in particular, of the solar neighbourhood and the disc of our Galaxy, in the light of recent theoretical and observational results. We explore the implications of this understanding for studies of `cosmic chemical evolution'.

Light isotopes of hydrogen and helium formed minutes after the Big Bang. The study of one of these primordial isotopes, helium-3, has now been proposed as a useful strategy for constraining the physics of the standard cosmological model.

We propose an expression for the star formation rate in spiral galaxies and a model of chemical evolution with a minimal number of adjustable parameters. Our model accounts for most of the relevant data in the Milky Way. By adopting our Galaxy as a prototype, we are able to derive cosmological implications for the comoving star formation rate, gas amount, gaseous abundances, and supernova rates as a function of redshift.

Compact binary mergers (of double neutron star and black hole-neutron star systems) are suggested to be the major site of the r-process elements in the Galaxy by recent hydrodynamical and nucleosynthesis studies. It has been pointed out, however, that estimated long lifetimes of compact binaries are in conflict with the presence of r-process-enhanced stars at the metallicity [Fe/H] ∼ −3. To resolve this problem, we examine the role of compact binary mergers in the early Galactic chemical evolution on the assumption that our Galactic halo was formed from merging sub-halos. The chemical evolutions are modeled for sub-halos with their total stellar masses between 104M⊙ and 2 × 108M⊙. The lifetimes of compact binaries are assumed to be 100 Myr (95%) and 1 Myr (5%) according to recent binary population synthesis studies. We find that the r-process abundances (relative to iron; [r/Fe]) start increasing at [Fe/H] ≤ −3 if the star formation rates are smaller for less massive sub-halos. Our models also suggest tha...

The chemical evolution of the disk of our Galaxy is studied with numerical models assuming infall and a radially varying star formation rate (SFR). We propose a model with a minimal set of physically plausible assumptions which satisfies the main observational constraints of the disk, including those of the solar neighborhood. Among them, the recent evidence for a negligible oxygen gradient in the outer Galaxy constrains severely some of the suggested SFR. We find that the resulting deuterium graidents are very sensitive to the past history of the disk; when detected by future experiments (like ISO and FUSE-LYMAN) they could be used to discriminate between some of the proposed histories. Finally, in the framework of our model we study the evolution of the carbon and oxygen isotopes in the Galaxy using the most recent stellar yields. We find that the evolution of 13C and 17O is relatively well understood (the former requiring some “primary” contribution, presumably from “hot-bottom burning” in intermediate mass stars), while a major puzzle still remains with the evolution of 18O.

International audience; We study radial migration and chemical evolution in a bar-dominated disc galaxy, by analysing the results of a fully self-consistent, high-resolution N-body+smoothed particle hydrodynamics (SPH) simulation. We find different behaviours for gas and star particles. Gas within corotation is driven in the central regions by the bar, where it forms a pseudo-bulge (discy-bulge), but it undergoes negligible radial displacement outside the bar region. Stars undergo substantial radial migration at all times, caused first by transient spiral arms and later by the bar. Despite the important amount of radial migration occurring in our model, its impact on the chemical properties is limited. The reason is the relatively flat abundance profile, due to the rapid early evolution of the whole disc. We show that the implications of radial migration on chemical evolution can be studied to a good accuracy by post-processing the results of the N-body+SPH calculation with a simple chemical evolution model having detailed chemistry and a parametrized description of radial migration. We find that radial migration impacts on chemical evolution both directly (by moving around the long-lived agents of nucleosynthesis, like e.g. SNIa or asymptotic giant branch stars, and thus altering the abundance profiles of the gas) and indirectly (by moving around the long-lived tracers of chemical evolution and thus affecting stellar metallicity profiles, local age-metallicity relations and metallicity distributions of stars, etc.).

Long Gamma Ray Bursts (LGRBs) are related to the final stages of evolution of massive stars. As such, they should follow the star formation rate (SFR) of galaxies. We can use them to probe for star-forming galaxies (SFGs) in the distant universe following this assumption. The relation between the rate of LGRBs in a given galaxy and its SFR (that we call the LGRB "bias") may be complex, as we have indications that the LGRB hosts are not perfect analogues to the general population of SFGs. In this work, we try to quantify the dependence of the LGRB bias on physical parameters of their host galaxy such as the SFR or the stellar mass. We propose an empirical method based on the comparison of stellar mass functions (and SFR distributions) of LGRB hosts and of SFGs in order to find how the bias depends on the stellar mass or the SFR. By applying this method to a sample of LGRB hosts at redshifts lower than 1.1, where the properties of SFGs are well established, and where the properties of LGRB host galaxies can be deduced from observations (for stellar masses larger than 10**9.25 Msun and SFR larger than 1.8 Msun / yr), we find that the LGRB bias depends on both the stellar mass and SFR. We find that the bias decreases with the SFR, i.e. we see no preference for highly SFGs, once taken into account the larger number of massive stars in galaxies with larger SFR. We do not find any trend with the specific star formation rate (SSFR) but the dynamical range in SSFR in our study is narrow. Although through an indirect method, we relate these trends to a possible decrease of the LGRBs rate / SFR ratio with the metallicity. The method we propose suggests trends that may be useful to constrain models of LGRB progenitors, showing a clear decrease of the LGRB bias with the metallicity. This is promising for the future as the number of LGRB hosts studied will increase., 9 pages, 5 figures, accepted in A&A

26 Al is the first cosmic radioactivity ever detected, more than ten years ago, through its characteristic 1.8 MeV gamma-ray line. Its ≈10 6 yr lifetime, much shorter than the ≈10 10 yr of galactic evolution, convincingly demonstrates that nucleosynthesis is currently active in our Galaxy. Current models of nucleosynthesis are still too uncertain to allow identification of the sites of that nucleosynthetic activity, despite their continuous improvement in the past ten years. The recent results of the Compton Gamma-Ray Observatory shed, for the first time, some light on the origin of galactic 26 Al, favoring massive stars as the main sources. The various measurements of 1.8 MeV emission and the theoretical models of 26 Al sources are presented in this review, along with the implications of the latest results for nuclear, stellar and galactic astrophysics.

Observations of metal-poor stars show intrinsic large dispersions in their chemical abundances. This may indicate that these stars are enriched by only one or a few supernovae, since the inter-stellar gas was not mixed enough at the early epoch. We construct an inhomogeneous chemical evolution model, and compare predicted stellar abundance distributions for OZn with observations. Using statistical method, we show clear differences between two sets of yields; by Nomoto et al. (1997) and by Woosley & Weaver (1995) .

In this paper, we present some statistical results of the various cross correlations among observed element abundances (both absolute values and ratios), neutral hydrogen column density and metal column density. Specifically, we point out the anti-correlations between the observed abundance ratios and metal column density in DLAs, namely, [X/Zn] and/or [X/Si] (where X stands for the refractories Fe, Cr and Ni) with [Zn/H]+log(N HI ) and [Si/H]+log(N HI ). We suggest that those identified anti-correlations could provide important clues to the dust depletion and nucleosynthetic patterns in DLAs.