ALBERT

Description: We have derived the abundances of 36 chemical elements in one Cepheid star, ASAS 181024-2049.6, located R G = 2.53 kpc from the Galactic Centre. This star falls within a region of the inner thin disc poorly sampled in Cepheids. Our spectral analysis shows that iron, magnesium, silicon, calcium and titanium local thermodynamic equilibrium abundances in that star support the presence of a plateau-like abundance distribution in the thin disc within 5 kpc of the Galactic Centre, as previously suggested by Martin et al. If confirmed, the flattening of the abundance gradient within that region could be the result of a decrease in the star formation rate due to dynamic effects, possibly from the central Galactic bar.

Description: We have investigated the diffuse interstellar band (DIB) at 661.3 nm seen in the spectra of Cepheid stars. After removal of the blending lines of ionized yttrium and neutral iron, we determined the equivalent widths (EWs) of the DIB and used these values to investigate the E ( B  –  V )–DIB EW relation. The relation found from Cepheids matches that found in B stars. This relation can help to find the reddening for newly discovered Cepheids without extensive photometric data, and thus determine their distances. The relation between E ( B  –  V ) and the DIB EW does not yield precise reddening values. It is not a substitute for better photometric or spectroscopic methods. At best, it is indicative, but it provides some information that may not be otherwise available. Defining R * = E ( B  –  V )/DIB EW, which we consider to be the analogue of R = E ( B  –  V )/ A v , we investigated the Galactic longitudinal dependence of R * assuming that the DIB EW value is representative of the interstellar absorption A v . We found that there is an apparent increase of the R * value that corresponds to the abnormal absorption seen towards Cygnus constellation. Finally, we constructed a 2D map of the DIB EW distribution in the Galactic disc basing on our rather limited sample of 253 spectra of 176 Cepheids.

Description: We derived elemental abundances in 27 Cepheids, the great majority situated within a zone of Galactocentric distances ranging from 5 to 7 kpc. One star of our sample, SU Sct, has a Galactocentric distance of about 3 kpc, and thus falls in a poorly investigated region of the inner thin disc. Our new results, combined with data on abundances in the very central part of our Galaxy taken from the literature, show that iron, magnesium, silicon, sulphur, calcium and titanium local thermodynamic equilibrium abundance radial distributions, as well as non-local thermodynamic equilibrium distribution of oxygen reveal a plateau-like structure or even positive abundance gradient in the region extending from the Galactic Centre to about 5 kpc.

Description: 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.

Description: We performed a non-local thermodynamic equilibrium (NLTE) analysis of the infrared oxygen triplet for a large number of Cepheid spectra obtained with the Hobby–Eberly Telescope. These data were combined with our previous NLTE results for stars observed with the Max Planck Gesellschaft Telescope with the aim of investigating the oxygen abundance distribution in the Galactic thin disc. We found the slope of the radial (O/H) distribution to be equal –0.058 dex kpc –1 . However, we found some evidence that the distribution might become flatter in the outer parts of the disc. This is supported by the results of other authors who have studied open clusters, planetary nebulae and H ii regions. Some mechanisms of flattening are discussed.

Description: Based on our prior accurate determination of fundamental parameters for 36 Galactic A-, F- and G-type supergiants and bright giants (luminosity classes I and II), we undertook a non-LTE analysis of the carbon abundance in their atmospheres. It is shown that the non-LTE corrections to the C abundances derived from C i lines are negative and increase with the effective temperature T eff ; the corrections are especially significant for the infrared C i lines with wavelengths 9060–9660 Å. The carbon underabundance as a general property of the stars in question is confirmed; a majority of the stars studied has the carbon deficiency [C/Fe] between –0.1 and –0.5 dex, with a minimum at –0.7 dex. When comparing the derived C deficiency with the N excess found by us for the same stars earlier, we obtain a pronounced N versus C anticorrelation, which could be expected from predictions of the theory. We found that the ratio [N/C] spans mostly the range from 0.3 to 1.7 dex. Both these enhanced [N/C] values and the C and N anomalies themselves are an obvious evidence of the presence on a star's surface of mixed material from stellar interiors; so, a majority of programme stars passed through the deep mixing during the main sequence (MS) and/or the first dredge-up (FD) phase. Comparison with theoretical predictions including rotationally induced mixing shows that the stars are either post-MS objects with the initial rotational velocities V 0  = 200–300 km s –1 or post-FD objects with V 0  = 0–300 km s –1 . The observed N versus C anticorrelation reflects a dependence of the C and N anomalies on the V 0 value: on average the higher V 0 the greater the anomalies. It is shown that an absence of detectable lithium in the atmospheres of the stars, which is accompanied with the observed N excess and C deficiency, is quite explainable.

Description: Recently, an increasing number of studies were devoted to measure the abundances of neutron-capture elements heavier than iron in stars belonging to Galactic Open Clusters (OCs). OCs span a sizeable range in metallicity (–0.6 ≤ [Fe/H] ≤ +0.4), and they show abundances of light elements similar to disc stars of the same age. A different pattern is observed for heavy elements. A large scatter is observed for Ba, with most OCs showing [Ba/Fe] and [Ba/La] overabundant with respect to the Sun. The origin of this overabundance is not clearly understood. With the goal of providing new observational insights, we determined radial velocities, atmospheric parameters and chemical composition of 27 giant stars members of five OCs: Cr 110, Cr 261, NGC 2477, NGC 2506 and NGC 5822. We used high-resolution spectra obtained with the UVES spectrograph at European Southern Observatory Paranal. We perform a detailed spectroscopic analysis of these stars to measure the abundance of up to 22 elements per star. We study the dependence of element abundance on metallicity and age with unprecedented detail, complementing our analysis with data culled from the literature. We confirm the trend of Ba overabundance in OCs, and show its large dispersion for clusters younger than ~4 Gyr. Finally, the implications of our results for stellar nucleosynthesis are discussed. We show in this work that the Ba enrichment compared to other neutron-capture elements in OCs cannot be explained by the contributions from the slow neutron-capture process and the rapid neutron-capture process. Instead, we argue that this anomalous signature can be explained by assuming an additional contribution by the intermediate neutron-capture process.

Description: Barium is a neutron-capture element that, in open clusters, is frequently overabundant with respect to iron. A clear explanation for this is still missing. Additionally, its gradient across the Galactic disc is poorly constrained. We measure the abundance of yttrium and barium using the synthetic spectrum method from UVES high-resolution spectra of eight distant open clusters, namely Ruprecht 4, Ruprecht 7, Berkeley 25, Berkeley 73, Berkeley 75, NGC 6192, NGC 6404 and NGC 6583. The barium abundance was estimated using non-local thermodynamic equilibrium approximation. We confirm that barium is indeed overabundant in most clusters, especially young clusters. Finally, we investigated the trend of yttrium and barium abundances as a function of distance in the Galaxy and ages. Several scenarios for the barium overabundance are then discussed.

Description: We derived the barium atmospheric abundances for a large sample of Cepheids, comprising 270 stars. The sample covers a large range of Galactocentric distances, from about 4 to 15 kpc, so it is appropriate to investigate the existence of radial barium abundance gradients in the Galactic disc. In fact, this is the first time that such a comprehensive analysis of the distribution of barium abundances in the Galactic disc has been carried out. As a result, we conclude that the Ba abundance distribution can be characterized by a zero gradient. This result is compared with derived gradients for other elements, and some reasons are briefly discussed for the independence of the barium abundances from Galactocentric distances.

Description: Using an Non-Local Thermodynamic Equilibrium (NLTE) analysis and a homogenous spectral data base, we have determined Ba abundances in a sample of 210 Galactic Cepheids and related objects. We confirm the previous result reported in Andrievsky et al. that the barium distribution in the range of Galactocentric distances from 5 to 18 kpc shows very small gradient value. The value determined here – d[Ba/H]/d R  –0.01 dex kpc –1 – is smaller than that for other s-process elements, such as La, Pr, Nd and Sm (Luck & Lambert), that typically show gradients of –0.03 dex kpc –1 .