Abstract. Modelling stellar atmospheres becomes increasingly demanding as more accurate observations draw a more complex picture of how real stars look like. What could be called a normal star becomes increasingly rare because of, e.g., significant deviations from the classical solar abundance pattern and clear evidence for stratification of elements in the atmospheres as well as surface inhomogeneities (spots) causing further severe deviations from "standard" atmospheres. We describe here a new code for calculating LTE plane-parallel stellar model atmospheres for early and intermediate type of stars which has been written in Compaq Fortran 95 and can be compiled for Windows and Linux/UNIX computer platforms. The code is based on modified 9 subroutines (Kurucz) and on spectrum synthesis codes written by V. Tsymbal with the main modifications of input physics concerning the block for opacity calculation. Each line contributing to opacity is taken into account for modelling the atmosphere, similar to synthetic spectrum calculations. This approach, which we call the line-by-line (LL) technique, avoids problems resulting from statistical methods (ODF, OS) and allows to calculate complex models with abundances which are not simply scaled from a standard pattern (usually the solar abundances) and which can be even depth dependent. Stratification is considered in this context as an empirical input parameter which has to be derived from observations. Due to the implemented numerical methods, mainly in the opacity calculation module, our code produces model atmospheres with modern PCs in a time comparable to that required by classical routines.
Abstract. We present the evidence for abundance stratification in the atmosphere of the rapidly oscillating Ap star γ Equ. Ca, Cr, Fe, Ba, Si, Na seem to be overabundant in deeper atmospheric layers, but normal to underabundant in the upper layers with a transition in the typical line forming region of −1.5 < log τ5000 < −0.5. This stratification profile agrees well with diffusion theory for Ca and Cr, developed for cool magnetic stars with a weak mass loss of ≈2.5 × 10 −15 M yr −1 . Pr and Nd from the rare earth elements have an opposite profile. Their abundance is more than 6 dex higher above log τ5000 ≈ −8.0 than in the deeper atmospheric layers. We further discuss the implications of abundance stratification in the context of radial velocity amplitudes and phases observed by Kochukhov & Ryabchikova (2001) for a variety of spectral lines and elements using high spectral and time resolved, high S/N observations.
Abstract.To reliably determine the spectroscopic signature of rapidly oscillating chemically peculiar (roAp) stars it is also necessary to investigate a sample of non pulsating chemically peculiar (noAp) as well as presumably "normal" stars. We describe in this study the sample of spectroscopically investigated stars and comment on the techniques used for the analysis. In particular we discuss ionization disequilibria of rare earths in roAp stars that distinguish them from noAp stars. In the light of the recently discovered pulsation of β CrB we see arguments that all magnetic CP2 stars up to a transition temperature of about 8100 K may be pulsating.
Abstract.We report results of the spectroscopic monitoring of the roAp star γ Equ with the ESO 3.6-m telescope. During 1.5 hours of observations a series of very high-resolution and high S/N spectra was obtained for this star in the 6138-6165Å spectral region. Short exposure times allowed us to resolve changes of γ Equ line profiles due to the rapid pulsations and to follow profile variations over 5 oscillation cycles. From this unique observational material information on amplitudes and phase shifts of radial velocity (RV) variations was extracted for 29 lines of 17 individual ions. We confirmed that spectral lines of rare-earth elements (REE) have the largest pulsation amplitudes, reaching up to 0.8 km s −1 . Moreover, we detected a phase shift between RV variations of singly and doubly ionized REE, discovered significant RV shifts of weak Na i lines and analysed line profile variations of Pr iii and Nd iii spectral features. This rich observational material opens a possibility to obtain a detailed picture of the vertical stratification of chemical elements and extract the main characteristics of the pulsational mode(s). In our observations we did not find support for the existence of the unique dependence of RV amplitude on line strength suggested in earlier spectroscopic studies of roAp stars. Instead, we argue that the individuality of the variations of all ions is a result of the complex interplay between inhomogeneous vertical and horizontal distributions of chemical elements and individual pulsation modes of γ Equ. We show that the extra line broadening observed in γ Equ spectrum is most likely caused by pulsations. A detailed analysis of Pr iii and Nd iii line profile variations resulted in the estimate of = 2 or 3, m = − or − + 1 and vp ≈ 10 km s −1 for the p-mode of the main pulsation frequency.
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