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 1.93m 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 progenito

Enrichment of the Galactic disc with neutron-capture elements: Gd, Dy, and Th

The study of the origin of heavy elements is one of the main goals of nuclear astrophysics. In this paper, we present new observational data for the heavy r-process elements gadolinium (Gd, Z= 64), dysprosium (Dy, Z= 66), and thorium (Th, Z= 90) in a sample of 276 Galactic disc stars (-1.0 < [Fe/H] < + 0.3). The stellar spectra have a high resolution of 42 000 and 75 000, and the signal-to-noise ratio higher than 100. The LTE abundances of Gd, Dy, and Th have been determined by comparing the observed and synthetic spectra for three Gd lines (149 stars), four Dy lines (152 stars), and the Th line at 4019.13 angstrom (170 stars). For about 70 per cent of the stars in our sample, Gd and Dy are measured for the first time, and Th for 95 per cent of the stars. Typical errors vary from 0.07 to 0.16 dex. This paper provides the first extended set of Th observations in the Milky Way disc. Together with europium (Eu, Z= 63) data from our previous studies, we have compared these new observations with nucleosynthesis predictions and Galactic Chemical Evolution simulations. We confirm that [Gd/Fe] and [Dy/Fe] show the same behaviour of Eu. We study with GCE simulations the evolution of [Th/Fe] in comparison with [Eu/Fe], showing that unlike Eu, either the Th production is metallicity dependent in case of a unique source of the r-process in the Galaxy, or the frequency of the Th-rich r-process source is decreasing with the increase in [Fe/H]

The NLTE Barium Abundance in Dwarf Stars in the Metallicity Range of -1 < [Fe/H] < +0.3

We present the results of determination of the barium abundance considering the non-LTE (NLTE) effects in 172 dwarf stars in the metallicity range of -1< [Fe/H] <+0.3, assigned to different Galactic substructures by kinematic criteria. We used a model of the Ba atom with 31 levels of Ba I and 101 levels of Ba II. The atmosphere models for the investigated stars were computed using the ATLAS9 code modified by new opacity distribution functions. The NLTE profiles of the unblended Ba II (4554 A, 5853 A, 6496 A) were computed and then compared to those observed. The line 6141 A was also used, but with an allowance for its correlation with the iron line. The average barium abundances in the thin and thick discs are 0.01 +/- 0.08 and -0.03 +/- 0.07, respectively. The comparison to the calculations of the Galactic chemical evolution by Serminato et al. (2009) was conducted. The trend obtained for the Ba abundance versus [Fe/H] suggests a complex barium production process in the thin and thick discs

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

MANGANESE ABUNDANCES IN THE ATMOSPHERE OF CLUMP GIANTS

The manganese abundances was determined in the atmospheres of clump giants stars whose election was made earlier based on their chemical composition and evolutionary tracks. The spectra of the studied stars were obtained using the facilities of the 1.93m  telescope of the Haute-Provence Observatoire (France) equipped with the échelle spectrograph ELODIE (R = 42000, S/N = ~100–300). The Mn abundances was determined under the LTE approximation by the synthetic spectrum approach with a detailed consideration of the superfine structure. The behaviour of manganese abundances with metallicity [Fe/H] was considered. The manganese abundances was determined in the atmospheres of clump giants stars whose election was made earlier based on their chemical composition and evolutionary tracks. The spectra of the studied stars were obtained using the facilities of the 1.93m  telescope of the Haute-Provence Observatoire (France) equipped with the échelle spectrograph ELODIE (R = 42000, S/N = ~100–300). The Mn abundances was determined under the LTE approximation by the synthetic spectrum approach with a detailed consideration of the superfine structure. The behaviour of manganese abundances with metallicity [Fe/H] was considered.

STRONTIUM ABUNDANCES IN COOL DWARF STARS OF GALACTIC THIN AND THICK DISKS

We revise the strontium abundances in FGK stars with metallicities ranging from −1.0 &lt; [Fe/H] &lt; +0.3. The observed stars belong to the substructures of the Galaxy thick and thin discs. The observations were conducted using the1.93 mtelescope at Observatoire de Haute-Provence (OHP, France) equipped with the echelle type spectrographs ELODIE and SOPHIE. The values of the Sr abundance were obtained using synthetic spectra using LTE model atmosphere. The comparison of our data with models of chemical evolution was made.

Europium abundances in cool dwarf stars of the galactic thick and thin disks

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