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Abstract

In the deeper layers of hot stellar photospheres the Stark widths of spectral lines can be comparable and even larger than the thermal Doppler widths. Using the semiclassical perturbation method, we investigate the influence of the collisions with charged particles for the In III lines. We determine a number of Stark broadening parameters important in the atmospheres of A-type stars and white dwarfs. Also, the obtained results are compared with the available experimental data. The results will be included in the STARK-B database, the Virtual Atomic and Molecular Data Center and the Serbian Virtual Observatory.

Abstract

The physical parameters of the atmosphere and its chemical composition for a post-AGB star HD 187885 are determined from high resolution spectra. The effective temperature T eff = 8000 ± 200 K and the surface gravity log g = 1.0 ± 0.3 were derived. The star was found to be metal-deficient with [Fe/H] = −0.51. The α-elements, except of Ca and Ti, and the s-process elements are overabundant. These results partly confirm and supplement the data available in the literature. The spectrum shows many circumstellar lines formed in the multiple expanding shells. Numerous diffuse interstellar bands seen in the spectra may also originate in the same shells.

Abstract

The high resolution spectra of hydrogen-deficient binary υ Sgr are analyzed. The atmospheric parameters are Teff = 12300±200 K, log g = 2:5±0:5 and ξt = 5 - 15 kms−1 depending on the element. For Fe II ξt = 9:3 ± 0:3 kms−1. Iron is slightly underabundant (-0.2 dex). Nitrogen is overabundant with [N/Fe]ͬ ≈ 1.0, carbon and oxygen are underabundant with [C/Fe] ≈ -1.6 and [O/Fe] ≈ -1.1. The s-process elements Y, Zr and Ba are overabundant about 0.5 dex. Quite large number of emission lines, both permitted and forbidden, originating from low excitation levels of neutral and ionized metals, are identified. Radial velocities of these emission lines indicate that an accretion disk in the system is present.

Abstract

High resolution spectra of M-type supergiant μ Cep are analyzed. The movements in the atmosphere of this star are highly supersonic and variable with depth. The lines forming in deeper layers show the widths corresponding to 30 kms−1. The lines forming in outer layers are much wider, 50 kms−1. At the same time, the microturbulent velocity (ξt) is low, from 4.0 to 4.5 kms−1. The atmosphere of μ Cep is slightly metal deficient with [Fe/H]≈-0.4.

Abstract

A high resolution spectrum of a pre-main sequence star HD 377 is analyzed. The atmospheric parameters are found to be: Teff =5875 K, log g = 4.25 and the microturbulent velocity ξt = 1.40 kms−1. The metallicity of HD377 is slightly higher than of the Sun, [Fe/H]=0.21. The lithium abundance is very high log ε(Li) = 3.02.

Abstract

We analyzed some new high resolution optical spectra of the semiregular RV Tauri-type star R Sct. Fundamental parameters were found to be T eff = 4500 K, log g = 0.0 and ξ t = 4.0 km s−1. The results of chemical analysis show that R Sct is a metal-poor star with [Fe/H]≈ −0.5. The carbon content with respect to iron is significantly larger than in the Sun, [C/Fe]=0.84, but there is an evident deficiency of heavy elements. We found no tight correlation of the chemical abundances on the condensation temperatures of elements. This means that in R Sct the depletion by condensation into dust does not work, with possible exception of Ca and Sc. The luminosity derived from the Hipparcos parallax corresponds to a tip of the red-giant branch or slightly above it. Thus it is possible that R Sct evolved off the early-AGB when it has not yet experienced the third dredge-up in thermal pulses, or it is still located on AGB. The peculiarities of spectral features (emissions, line-splitting) and the complicated time-variable radial velocities were also studied.

Abstract

High resolution spectra of the extremely metal-poor star HD 52961 are investigated. The atmospheric parameters found are: T eff = 6000 ± 100 K, log g = 0.5±0.5, ξ t = 6.8 km s−1, [Fe/H] = −4.50±0.20. The carbon abundance is close to the solar one, [C/H] = −0.17±0.12. At the same time abundances of heavy refractory elements are very low. The chemical composition and atmospheric parameters have not changed compared to the first observations of the star about 20 years ago, contrary to expectation of dissolving the peculiarities by mass-loss during a relatively short time. We also find evidence of ongoing mass-loss in this post-AGB star with a rate of ≈ 5 · 10−6 M yr−1.

Abstract

Diffusional separation of calcium isotopes in the atmospheres of hot chemically peculiar stars is studied. In addition to the usual radiative acceleration effect, the light-induced drift is taken into account. We propose that microturbulence in stable stellar atmospheres is generated by the interaction between plasma particles and radiative flux. Formulae for the microturbulent velocity and microturbulence diffusion coefficient are derived. Data on isotopic and hyperfine splitting of the calcium spectral lines have been collected as an input file. The equilibrium Ca isotope concentrations are found in model computations, iteratively correcting the radiative acceleration values. The general picture of Ca isotope stratification is found to be similar to our previous results obtained for Hg isotopes: dominating overabundance of the heaviest isotope. Diffusional stratification of Ca isotope concentrations in atmospheres of late B and early A spectral types are computed and visualized in figures. The isotope abundances on the inner boundary surface were fixed to be the solar ones. The computed Ca II infrared triplet line profiles are compared with the observed line profiles in a high-dispersion spectrum of HD 175640.

Abstract

In the framework of the Virtual Observatory, the newly developed service TheoSSA provides access to theoretical stellar spectral energy distributions. In a pilot phase, this service is based on the well-established Tübingen NLTE Model-Atmosphere Package for hot, compact stars. We demonstrate its present capabilities and future extensions.

Abstract

In the present study we had three main aims. First to study the possibility of reducing the initial model atmosphere data to short analytical polynomials. The second was to use as the depth variable the logarithm of the local gas pressure instead the Rosseland mean. The third aim was to check the applicability of the derived formulae and proposed computation methods to obtain high precision self-consistent results in modeling hot plane-parallel stellar atmospheres. Introducing the dimensionless (reduced) local quantities θ = T/T eff and β = P/P(T eff) it has been shown that for hot convection-free stellar atmospheres the curves log θ versus log β reduce an initial grid of models to simple polynomials and bring forth some general features of the model stellar atmospheres. Even for stellar atmospheres having the convective zones in the deeper atmospheric layers, the outer part of the atmosphere (up to T = T eff and for T eff > 5000 K) can be described in the same manner by curves log θ versus log β as for the hotter stars. Iterative modeling of any hot stellar atmosphere can be started from these formulae (obtained for solar abundances), using rational polynomial ratios for P(T eff), obtaining from these data the needed T versus P dependence. To check suitability of the formulae, the iterative correction of the model stellar atmospheres has been carried out by the traditional Unsöld-Lucy method and by the novel least squares optimization based on Levenberg-Marquardt method, followed by Broyden correction loop. It has been shown that the flux constancy obtained by it is almost 2 dex higher than obtained by the Unsöld-Lucy method. The precision estimators as criteria of the modeling algorithms self-consistency and of the computational precision level have been proposed and used.