Non-LTE analysis of copper abundances for the two distinct halo populations in the solar neighborhood

Two distinct halo populations were found in the solar neighborhood by a series of works. They can be clearly separated by [alpha\Fe] and several other elemental abundance ratios including [Cu/Fe]. Very recently, a non-local thermodynamic equilibrium (non-LTE) study revealed that relatively large departures exist between LTE and non-LTE results in copper abundance analysis. We aim to derive the copper abundances for the stars from the sample of Nissen et al (2010) with both LTE and non-LTE calculations. Based on our results, we study the non-LTE effects of copper and investigate whether the high-alpha population can still be distinguished from the low-alpha population in the non-LTE [Cu/Fe] results. Our differential abundance ratios are derived from the high-resolution spectra collected from VLT/UVES and NOT/FIES spectrographs. Applying the MAFAGS opacity sampling atmospheric models and spectrum synthesis method, we derive the non-LTE copper abundances based on the new atomic model with current atomic data obtained from both laboratory and theoretical calculations. The copper abundances determined from non-LTE calculations are increased by 0.01 to 0.2 dex depending on the stellar parameters compared with the LTE results. The non-LTE [Cu/Fe] trend is much flatter than the LTE one in the metallicity range -1.6<[Fe/H]<-0.8. Taking non-LTE effects into consideration, the high- and low-alpha stars still show distinguishable copper abundances, which appear even more clear in a diagram of non-LTE [Cu/Fe] versus [Fe/H]. The non-LTE effects are strong for copper, especially in metal-poor stars. Our results confirmed that there are two distinct halo populations in the solar neighborhood. The dichotomy in copper abundance is a peculiar feature of each population, suggesting that they formed in different environments and evolved obeying diverse scenarios.Comment: 9 pages, 7 figures, 2 table

Chemical composition of 90 F and G disk dwarfs

High resolution, high S/N spectra have been obtained for a sample of 90 F and G main-sequence disk stars covering the metallicity range -1.0 < [Fe/H] < +0.1, and have been analysed in a parallel way to the work of Edvardsson et al. (1993). Effective temperatures are based on the Alonso et al. (1996) calibration of color indices and surface gravities are calculated from Hipparcos parallaxes, which also allow more accurate ages to be calculated. In addition, more reliable kinematical parameters are derived from Hipparcos distances and proper motions. Finally, a larger spectral coverage, 5600 - 8800 A, makes it possible to improve the abundance accuracy by studying more lines and to discuss several elements not included in the work of Edvardsson et al. The present paper provides the data and discusses some general results of the abundance survey. A group of stars in the metallicity range of -1.0 < [Fe/H] < -0.6 having a small mean Galactocentric distance in the stellar orbits, Rm < 7 kpc, are shown to be older than the other disk stars and probably belong to the thick disk. Excluding these stars, a slight decreasing trend of [Fe/H] with increasing Rm and age is found, but a large scatter in [Fe/H] (up to 0.5 dex) is present at a given age and Rm. The derived trends of O, Mg, Si, Ca, Ti, Ni and Ba as a function of [Fe/H] agree rather well with those of Edvardsson et al., but the overabundance of Na and Al for metal-poor stars found in their work is not confirmed. Furthermore, the Galactic evolution of elements not included in Edvardsson et al., K, V and Cr, is studied.Comment: 16 pages with 10 figures. Accepted for publication in A&A

The puzzling abundance pattern of HD134439 and HD134440

Abundances of 18 elements are determined for the common proper-motion pair, HD134439 and HD134440, which shows high [Mn/Fe] and low [\alpha/Fe] ratios as compared to normal halo stars. Moreover, puzzling abundances are indicated from elements whose origins are normally considered to be from the same nucleosynthesis history. Particularly, we have found that [Mg/Fe] and [Si/Fe] are lower than [Ca/Fe] and [Ti/Fe] by 0.1-0.3 dex. When elemental abundances are interpreted in term of their condensation temperatures (Tc), obvious trends of [X/Fe] vs. Tc for alpha elements and probably iron-peak elements as well are shown. The hypothesis that these stars have formed from a dusty environment in dSph galaxy provides a solution to the puzzling abundance pattern.Comment: 13 pages,5 figures, MN, in pres

Comparative Genomics Reveals Key Gain-of-Function Events in Foxp3 during Regulatory T Cell Evolution

The immune system has the ability to suppress undesirable responses, such as those against commensal bacteria, food, and paternal antigens in placenta pregnancy. The lineage-specific transcription factor Foxp3 orchestrates the development and function of regulatory T cells underlying this immunological tolerance. Despite the crucial role of Foxp3 in supporting immune homeostasis, little is known about its origin, evolution, and species conservation. We explore these questions using comparative genomics, structural modeling, and functional analyses. Our data reveal that key gain-of-function events occurred during the evolution of Foxp3 in higher vertebrates. We identify key conserved residues in its forkhead domain and show a detailed analysis of the N-terminal region of Foxp3, which is only conserved in mammals. These components are under purifying selection, and our mutational analyses demonstrate that they are essential for Foxp3 function. Our study points to critical functional adaptations in immune tolerance among higher vertebrates, and suggests that Foxp3-mediated transcriptional mechanisms emerged during mammalian evolution as a stepwise gain of functional domains that enabled Foxp3 to interact with a multitude of interaction partners

Accerlerating acculturation through tacit knowledge flows: refining a grounded theory model

DOI 10.1108/03055721011071430Purpose - Intercultural knowledge flows are critical to global enterprise performance, but the impact of knowledge management theory on such intercultural flows remains limited. This paper seeks to address this issue

Galactic Cosmic Rays from Superbubbles and the Abundances of Lithium, Beryllium, and Boron

In this article we study the galactic evolution of the LiBeB elements within the framework of a detailed model of the chemical evolution of the Galaxy that includes galactic cosmic ray nucleosynthesis by particles accelerated in superbubbles. The chemical composition of the superbubble consists of varying proportions of ISM and freshly supernova synthesized material. The observational trends of 6 LiBeB evolution are nicely reproduced by models in which GCR come from a mixture of 25% of supernova material with 75% of ISM, except for 6 Li, for which maybe an extra source is required at low metallicities. To account for 7 Li evolution several additional sources have been considered (neutrino-induced nucleosynthesis, nova outbursts, C-stars). The model fulfills the energetic requirements for GCR acceleration.Comment: 25 pages, 9 figures. Accepted for publication in the Astrophysical Journa

Sulphur abundances in disk stars: A correlation with silicon

We have performed new determinations of sulphur and silicon abundances for a sample of 26 disk stars based on high-resolution, high signal-to-noise spectra. The results indicate a solar [S/Fe] for [Fe/H] > −0.3, below which [S/Fe] increases to ~0.25 dex at [Fe/H] = −1.0. We find that there is a good correlation between [S/H] and [Si/H], indicating the same nucleosynthetic origin of the two elements. It seems that the ratio of sulphur to silicon does not depend on metallicity for [Fe/H] > −1.0. The implications of these results on models for the nucleosynthesis of a-capture elements and the chemical evolution of the Galaxy are discussed. Based on observations carried out at National Astronomical Observatories (Xinglong, PR China)

The Chemical Compositions of the SRd Variable Stars-- II. WY Andromedae, VW Eridani, and UW Librae

Chemical compositions are derived from high-resolution spectra for three stars classed as SRd variables in the General Catalogue of Variable Stars. These stars are shown to be metal-poor supergiants: WY And with [Fe/H] = -1.0, VW Eri with [Fe/H] = -1.8, and UW Lib with [Fe/H] = -1.2. Their compositions are identical to within the measurement errors with the compositions of subdwarfs, subgiants, and less evolved giants of the same FeH. The stars are at the tip of the first giant branch or in the early stages of evolution along the asymptotic giant branch (AGB). There is no convincing evidence that these SRd variables are experiencing thermal pulsing and the third dredge-up on the AGB. The SRds appear to be the cool limit of the sequence of RV Tauri variables.Comment: 14 pages, 1 figure, 4 table