Related papers: Light chemical elements in stars: mysteries and un…
The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium1, almost all other elements were created in stars and supernovae. The mass fraction, Z, of elements more massive than helium, is called…
The element boron belongs, together with lithium and beryllium, to a known trio of important elements for the study of evolutionary processes in low mass stars. Because B is the least fragile of this trio to be destroyed in the stellar…
Methods to determine abundances of the elements in the atmospheres of F, G, and K stars with precisions of 0.01-0.03 dex are reviewed. Such high-precision stellar abundances have led to the discovery of unexpected phenomena and relations…
Recent advances on the quest to determine the primordial or pregalactic helium abundance, Yp, are reviewed. There are seven problems affecting the He/H abundance determinations of H II regions that are briefly discussed: the underlying…
We present an abundance analysis of light elements in He-rich stars. The analysis is based on both low and high resolution observations collected at ESO, La Silla, Chile in the optical region and includes 6 standards and 21 He-rich stars.…
We present stellar parameters of 19 K-type giants and their abundances of 13 chemical elements (Al, Ba, Ca, Fe, K, Mg, Mn, Na, Ni, Sc, Si, Ti and V), selected from two moving groups, covering the metallicity range of -0.6 < [Fe/H] < 0.2,…
The connection between helium-rich hot subdwarfs of spectral types O and B (He-sdB) has been relatively unexplored since the latter were found in significant numbers in the 1980's. In order to explore this connection further, we have…
Aims: Recent observations have challenged our understanding of rotational mixing in massive stars by revealing a population of fast-rotating objects with apparently normal surface nitrogen abundances. However, several questions have arisen…
We report a detailed abundance analysis for HE0107-5240, a halo giant with [Fe/H]_NLTE=-5.3. This star was discovered in the course of follow-up medium-resolution spectroscopy of extremely metal-poor candidates selected from the digitized…
Abundances of lithium, heavy elements and carbon isotope ratios have been derived in 12 J-type galactic carbon stars. The abundance analysis shows that in these stars the abundances of s-process elements with respect to the metallicity are…
The oldest stars in the universe retain to a great extent detailed information on the chemical composition of the interstellar medium at the time of their birth. Hence the earliest phases of Galactic chemical evolution and nucleosynthesis…
We have derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Ni and Ba for 43 metal-poor field stars in the solar neighbourhood with iron abundances [Fe/H] ranging from -0.4 to -3.0. Total abundance errors are estimated to about…
We present the results of a detailed NLTE abundance study of nine beta Cephei stars, all of them being prime targets for theoretical modelling: gamma Peg, delta Cet, nu Eri, beta CMa, xi1 CMa, V836 Cen, V2052 Oph, beta Cep and DD (12) Lac.…
Based on the high resolution and high signal-to-noise spectra, we derived the chemical abundances of 20 elements for 20 barium (Ba-) stars. For the first time, the detailed abundances of four sample stars, namely HD 92482, HD 150430, HD…
Based on a simple, but fairly successful, model of the chemical evolution of the Milky Way disk, we study the evolution of the abundances of the elements He, C, N, O, Ne, Mg, Al, Si, S, Ar and Fe. We use metallicity dependent yields for…
The chemical composition of stars with extremely low metal contents (taking ``metals'' to mean all elements other than hydrogen and helium) provides us with information on the masses of the stars that produced the first metals. Such a…
Theoretical prediction of surface stellar abundances of light elements -- lithium, beryllium, and boron -- represents one of the most interesting open problems in astrophysics. As well known, several measurements of 7-Li abundances in…
Helium abundances and atmospheric parameters have been determined from high resolution spectra for a new sample of 46 bright hot subdwarf B (sdB) stars. The helium abundances have been measured with high accuracy. We confirm the correlation…
The hydrogen-deficiency in extremely hot post-AGB stars of spectral class PG1159 is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse that consumes the hydrogen envelope, exposing the usually-hidden intershell…
Big Bang Nucleosynthesis is the theory of the production of the the light element isotopes of D, He3, He4, and Li7. After a brief review of the essential elements of the standard Big Bang model at a temperature of about 1 MeV, the…