Related papers: Stellar Iron Abundances: non-LTE Effects

The Galactic evolution of copper remains poorly understood, partly due to the strong departures from local thermodynamic equilibrium (LTE) affecting Cu I lines. A key source of uncertainty in non-LTE modelling is the treatment of inelastic…

We determined the silicon abundances of 253 metal-poor stars in the metallicity range $-4<\mathrm{[Fe/H]} <-1.5$, based on non-local thermodynamic equilibrium (NLTE) line formation calculations of neutral silicon and high-resolution spectra…

Spectra of unevolved metal-poor halo stars uniquely reflect the elemental abundances incorporated during the earliest Galactic epoch. Their heavy-element content is well understood as the products of neutron capture on iron-peak elements.…

Spectroscopically determined Li abundances of metal-poor turn-off dwarfs are known to be nearly constant (Spite plateau), but lower than the primordial value expected from the standard cosmological model. However, abundance determination by…

A non-LTE (NLTE) abundance analysis was carried out for three extreme helium stars (EHes): BD+10 2179, BD-9 4395, and LS IV+6 002, from their optical spectra with NLTE model atmospheres. NLTE TLUSTY model atmospheres were computed with H,…

Carbon abundances in late-type stars are important in a variety of astrophysical contexts. However C i lines, one of the main abundance diagnostics, are sensitive to departures from local thermodynamic equilibrium (LTE). We present a model…

A new model atom of Sc II was constructed using the most up-to-date atomic data. For the testing purpose, the non-local thermodynamic equilibrium (non-LTE) calculations were carried out for three stars with reliably determined atmospheric…

We present an analysis of the UVES high-resolution spectroscopic observations at the 8.2m VLT of J0023+0307, a main-sequence extremely iron-poor dwarf star. We are unable to detect iron lines in the spectrum but derive [Fe/H]<-6.1 from the…

We present theoretical iron emission line strengths for physical conditions typical of Active Galactic Nuclei with Broad-Line Regions. The non-local thermodynamic equilibrium (NLTE) models include a new and extensive treatment of radiative…

Quantitative analyses of extreme helium stars to date face the difficulty that theory fails to reproduce the observed helium lines in their entirety, wings and line cores. Here, we demonstrate how the issues can be resolved using…

Manganese (Mn) is a key Fe-group elements, commonly employed in stellar population and nucleosynthesis studies to explore the role of SN Ia. We have developed a new non-local thermodynamic equilibrium (NLTE) model of Mn, including new…

Based on an exteded grid of NLTE, line blanketed model atmospheres with stellar winds as calculated by means of FASTWIND, we have investigated the change in the strengths of strategic Helium transitions in the optical as caused by a 0.3…

We calculate a grid of spherically symmetric OB stellar atmospheres at low metallicities, including both non-local thermodynamic equilibrium (NLTE) and metal line blanketing effects. This is done to assess the uncertainties in helium…

Rate coefficients for inelastic collisions between Li and H atoms covering all transitions between the asymptotic states Li(2s,2p,3s,3p,3d,4s,4p,4d,4f)+H(1s) and Li^+ +H^- are presented for the temperature range 2000-8000 K based on recent…

Mg is often traced in late-type stars using lines of neutral magnesium, which is expected to be subject to departures from LTE. The astrophysical importance of Mg as well as its relative simplicity from an atomic physics point of view,…

I present here the main results of recent realistic, 3D, hydrodynamical simulations of convection at the surface of metal-poor red giant stars. I discuss the application of these convection simulations as time-dependent, 3D, hydrodynamical…

(abridged) We present deep spectroscopy of a large sample of low-metallicity emission-line galaxies. The main goal of this study is to derive element abundances in these low-metallicity galaxies. We analyze 121 VLT spectra of HII regions in…

Active galactic nuclei (AGN) have Fe II emission from the broad line region (BLR) that differs greatly in strength from object to object. We examine the role of the total and gas-phase iron abundance in determining Fe II strength. Using AGN…

We have performed accurate iron abundance measurements for 44 red giants (RGs) in the Carina dwarf spheroidal (dSph) galaxy. We used archival, high-resolution spectra (R~38,000) collected with UVES at ESO/VLT either in slit mode (5) or in…

The abundances of alkali elements (Li, Na, and K) were determined from the Li I 6708, Na I 5682/5688, and K I 7699 lines by taking into account the non-LTE effect for 24 sharp-lined A-type stars v sin i < 50 km/s, 7000 K < Teff <10000 K,…