Related papers: Pregalactic LiBeB Production by Supernova Cosmic R…
The very peculiar abundance patterns observed in extremely metal-poor (EMP) stars can not be explained by ordinary supernova nucleosynthesis but can be well-reproduced by nucleosynthesis in hyper-energetic and hyper-aspherical explosions,…
The most metal-poor stars found in the Galaxy and in nearby galaxies are witnesses of the early evolution of the Universe. In a general picture in which we expect the metallicity to increase monotonically with time, as a result of the metal…
Carbon (C) is thought to be produced by both core collapse supernovae (CCSN) and asymptotic giant branch (AGB) stars, but the relative contributions of these two sources are uncertain. We investigate the astrophysical origin of C using…
With abundances and 2{\sigma} upper limits of fluorine (F) in seven metal-poor field giants, nucleosynthesis of stellar F at low metallicity is discussed. The measurements are derived from the HF(1-0) R9 line at 23358{\AA} using…
A few topics concerning the early chemical evolution of the Milky Way are critically discussed. In particular, it is argued that: 1) Observed abundance patterns of extremely metal poor stars (of Pop. II) do not constrain the mass range of…
We have determined Be abundances in 50 F and G dwarfs in the mass range of 0.9 $\leq$ M$_\odot$ $\leq$ 1.1 as determined by Lambert & Reddy. The effective temperatures are 5600 to 6400 K and metallicities from $-$0.65 to +0.11. The spectra…
Since the pioneering observations of Spite & Spite in 1982, the constant lithium abundance of metal-poor ([Fe/H]<-1.3) halo stars near the turnoff has been attributed a cosmological origin. Closer analysis revealed that the observed…
The abundance patterns of metal-poor stars provide us a wealth of chemical information about various stages of the chemical evolution of the Galaxy. In particular, these stars allow us to study the formation and evolution of the elements…
In this paper we present a study of chemical abundances in six star-forming regions. Stellar parameters and metallicities are derived using high-resolution, high S/N spectra of weak-line T-Tauri stars in each region. The results show that…
Primordial or Big Bang nucleosynthesis (BBN) is one of the three historical strong evidences for the Big-Bang model together with the expansion of the Universe and the Cosmic Microwave Background radiation (CMB). The recent results by the…
There is continued interest in the possibility that big bang nucleosynthesis may produce significant quantities of Be and B. In this paper we reevaluate the primordial abundances taking into account uncertainties in reactions rates. We…
Massive stars played a key role in the early evolution of the Universe. They formed with the first halos and started the re-ionisation. It is therefore very important to understand their evolution. In this review, we first recall the effect…
We study the formation of low-mass and extremely metal-poor stars in the early universe. Our study is motivated by the recent discovery of a low-mass (M < 0.8 Msun) and extremely metal-poor (Z <= 4.5 x 10^{-5} Zsun) star in the Galactic…
The stellar evolution of lithium-rich (Li-rich) giant stars at very low metallicities remains largely unexplored to date. Using two recent large LAMOST catalogues of field, low-mass giant stars (both Li-rich and Li-poor) with metallicities…
We compute the evolution of the abundances of barium and europium in the Milky Way and we compare our results with the observed abundances from the recent UVES Large Program "First Stars". We use a chemical evolution model which already…
Very old halo stars were previously found to show at least four different abundance 'anomalies', which models of fast rotating massive stars (spinstars) can successfully account for: rise of N/O and C/O, low 12C/13C and a primary-like…
The most metal-poor stars in the Milky Way witnessed the early phases of formation of the Galaxy, and have chemical compositions that are close to the pristine mixture from Big Bang nucleosynthesis, polluted by one or few supernovae. Only…
We calculate presupernova evolutions and supernova explosions of massive stars (M=13-25 Mo) for various metallicities. We find the following characteristic abundance patterns of nucleosynthesis in the metal-free (Pop III) stars. (1) The…
We have obtained low-resolution near infrared spectra of three QSOs at 5.7 < z < 6.3 using the NICMOS instrument of the Hubble Space Telescope. The spectra cover the rest-frame ultraviolet emission of the objects between lambda_rest ~ 1600A…
Light curves, explosion energies, and remnant masses are calculated for a grid of supernovae resulting from massive helium stars that have been evolved including mass loss. These presupernova stars should approximate the results of binary…