T. I. Gorbaneva

Abundances of neutron-capture elements in stars of the Galactic disk substructures

Aims. The aim of this work is to present and discuss the observations of the iron peak (Fe, Ni) and neutron-capture element (Y, Zr, Ba, La, Ce, Nd, Sm, and Eu) abundances for 276 FGK dwarfs, located in the Galactic disk with metallicity −1 < [Fe/H] < +0.3. Methods. Atmospheric parameters and chemical composition of the studied stars were determined from an high resolution, high signal-to-noise echelle spectra obtained with the echelle spectrograph ELODIE at the Observatoire de Haute-Provence (France). Effective temperatures were estimated by the line depth ratio method and from the Hα line-wing fitting. Surface gravities (log g )w ere determined by parallaxes and the ionization balance of iron. Abundance determinations were carried out using the LTE approach, taking the hyperfine structure for Eu into account, and the abundance of Ba was computed under the NLTE approximation. Results. We are able to assign most of the stars in our sample to the substructures of the Galaxy thick disk, thin disk, or Hercules stream according to their kinematics. The classification of 27 stars is uncertain. For most of the stars in the sample, the abundances of neutron-capture elements have not been measured earlier. For all of them, we provide the chemical composition and discuss the contribution from different nucleosynthesis processes. Conclusions. The [Ni/Fe] ratio shows a flat value close to the solar one for the whole metallicity range, with a small scatter, pointing to a nearly solar Ni/Fe ratio for the ejecta of both core-collapse SN and SNIa. The increase in the [Ni/Fe] for metallicity higher than solar is confirmed, and it is due to the metallicity dependence of 56 Ni ejecta from SNIa. Under large uncertainty in the age determination of observed stars, we verified that there is a large dispersion in the AMR in the thin disk, and no clear trend as in the thick disk. That may be one of the main reasons for the dispersion, observed for the s-process elements in the thin disk (e.g., Ba and La), whereas much narrower dispersion can be seen for r-process elements (e.g., Eu). Within the current uncertainties, we do not see a clear decreasing trend of [Ba/ Fe] or [La/Fe] with metallicity in the thin disk, except maybe for super-solar metallicities. We cannot confirm an increase in the mentioned ratios with decreasing stellar age.

Mn abundances in the stars of the Galactic disc with metallicities-1.0 < [Fe/H] < 0.3

In this work, we present and discuss the observations of the Mn abundances for 247 FGK dwarfs, located in the Galactic disc with metallicity −1 < [Fe/H] < +0.3. The observed stars belong to the substructures of the Galaxy thick and thin disks, and to the Hercules stream. The observations were conducted using the 1.93 m telescope at Observatoire de Haute-Provence (OHP, France) equipped with the echelle-type spectrographs ELODIE and SOPHIE. The abundances were derived under the LTE approximation, with an average error for the [Mn/Fe] ratio of 0.10 dex. For most of the stars in the sample, Mn abundances are not available in the literature. We obtain an evolution of [Mn/Fe] ratio with the metallicity [Fe/H] consistent with previous data compilations. In particular, within the metallicity range covered by our stellar sample, the [Mn/Fe] ratio is increasing with the increase of metallicity. This due to the contribution to the Galactic chemical evolution of Mn and Fe from thermonuclear supernovae. We confirm the baseline scenario where most of the Mn in the Galactic disc and in the Sun is made by thermonuclear supernovae. In particular, the effective contribution from core-collapse supernovae to the Mn in the Solar system is about 10–20 per cent. However, present uncertainties affecting the production of Mn and Fe in thermonuclear supernovae are limiting the constraining power of the observed [Mn/Fe] trend in the Galactic discs on, e.g. the frequency of different thermonuclear supernovae populations. The different production of these two elements in different types of thermonuclear supernovae needs to be disentangled by the dependence of their relative production on the metallicity of the supernova progenitor.

The copper and zinc abundances in stars of galactic sub-structures

We have determined abundances of copper, zinc, sodium, and aluminum in the atmospheres of 172 F, G, and K dwarf stars (−1.0 < [Fe/H] < 0.3) belonging to the Galaxy’s thin and thick disks and to the Hercules moving group. Our observations were performed with the ELODIE échelle spectrometer on the 1.93-m telescope of the Haute Provence Observatory, with a resolving power of R = 42 000 and signal-to-noise ratio S/N > 100. The Na, Al, Cu, and Zn abundances were derived in an LTE approximation; the synthetic spectrum for the copper lines was calculated taking into account super-fine structure of the lines. We analyzed the abundances of these elements as a function of metallicity [Fe/H] for stars of the thin and thick disks of the Galaxy and the Hercules moving group. The Cu abundances and their trends with metallicity are essentially the same in the three studied sub-structures. The mean Al and Zn abundances for stars of the thin and thick disks differ significantly.

Observing the metal-poor solar neighbourhood: a comparison of galactic chemical evolution predictions

© 2017 The Authors. Atmospheric parameters and chemical compositions for 10 stars with metallicities in the region of -2.2 < [Fe/H] < -0.6 were precisely determined using high-resolution, high signal-tonoise, spectra. For each star, the abundances, for 14-27 elements, were derived using both local thermodynamic equilibrium (LTE) and non-LTE (NLTE) approaches. In particular, differences by assuming LTE or NLTE are about 0.10 dex; depending on [Fe/H], Teff, gravity and element lines used in the analysis. We find that the O abundance has the largest error, ranging from 0.10 and 0.2 dex. The best measured elements are Cr, Fe, and Mn; with errors between 0.03 and 0.11 dex. The stars in our sample were included in previous different observational work. We provide a consistent data analysis. The data dispersion introduced in the literature by different techniques and assumptions used by the different authors is within the observational errors, excepting for HD103095. We compare these results with stellar observations from different data sets and a number of theoretical galactic chemical evolution (GCE) simulations. We find a large scatter in the GCE results, used to study the origin of the elements. Within this scatter as found in previous GCE simulations, we cannot reproduce the evolution of the elemental ratios [Sc/Fe] , [Ti/Fe], and [V/Fe] at different metallicities. The stellar yields from core-collapse supernovae are likely primarily responsible for this discrepancy. Possible solutions and open problems are discussed.

NLTE barium abundance in thin and thick disks of the Galaxy

We present the determinations of the barium abundance takin g into account the non-LTE (NLTE) effects in 173 dwarf stars belonging to the thin and thick dis ks. The NLTE profiles of the unblended Ba II lines (4554, 5853, 6496 ÅÅ) have been computed a nd compared to the observed profiles. The line 6141 Å was also used, but taking into accoun t an influence of iron line. We used a modified version of the MULTI code and atomic model of Ba atom with 31 levels of Ba I, and 101 levels of Ba II. Atmosphere models of investigated stars h ve been calculated with ATLAS9 code (modified using the New Opacity distribution functions by Castelli & Kurucz). The obtained trend in the Ba abundance vs. [Fe/H] suggests a complex proce ss f the Ba production in the thin and thick disks.