This article reports some preliminary results on an analysis of line bisectors of metal absorption lines of RR Lyrae, the prototype of its class of pulsators. The extensive data set used for this study consists of a time series of spectra obtained at
various pulsation phases as well as different Blazhko phases. This setup should allow a comparison of the atmospheric behavior, especially of the function of radial velocity versus depth at differing Blazhko phases, but (almost) identical pulsation phase, making it possible to investigate whether the modulation causes a change in the atmospheric motion of RR Lyrae. While the nature of the Blazhko modulation has often been investigated photometrically and described as a change in the light curve, studies on time series of high resolution spectra are rare. We present for the first time work on line bisectors at different phases of RR Lyr.
The knowledge of accurate stellar parameters is a keystone in several fields of stellar astrophysics, such as asteroseismology and stellar evolution. Although the fundamental parameters can be derived both from spectroscopy and multicolour photometry
, the results obtained are sometimes affected by systematic uncertainties. In this paper, we present a self-consistent spectral analysis of the pulsating star RR Lyr, which is the primary target for our study of the Blazhko effect. We used high-resolution and high signal-to-noise ratio spectra to carry out a consistent parameter determination and abundance analysis for RR Lyr. We provide a detailed description of the methodology adopted to derive the fundamental parameters and the abundances. Stellar pulsation attains high amplitudes in RR Lyrae stars, and as a consequence the stellar parameters vary significantly over the pulsation cycle. The abundances of the star, however, are not expected to change. From a set of available high-resolution spectra of RR Lyr we selected the phase of maximum radius, at which the spectra are least disturbed by the pulsation. Using the abundances determined at this phase as a starting point, we expect to obtain a higher accuracy in the fundamental parameters determined at other phases. The set of fundamental parameters obtained in this work fits the observed spectrum accurately. Through the abundance analysis, we find clear indications for a depth-dependent microturbulent velocity, that we quantified. We confirm the importance of a consistent analysis of relevant spectroscopic features, application of advanced model atmospheres, and the use of up-to-date atomic line data for the determination of stellar parameters. These results are crucial for further studies, e.g., detailed theoretical modelling of the observed pulsations.
In the last few years we have developed stellar model atmospheres which included effects of anomalous abundances and strong magnetic field. The full treatment of anomalous Zeeman splitting and polarized radiative transfer were introduced in the model
atmosphere calculations for the first time. In this investigation we present results of modelling the atmosphere of one of the most extreme magnetic chemically peculiar stars, HD137509. This Bp SiCrFe star has the mean surface magnetic field modulus of about 29kG. We use the recent version of the line-by-line opacity sampling stellar model atmosphere code LLmodels, which incorporates the full treatment of Zeeman splitting of spectral lines, detailed polarized radiative transfer and arbitrary abundances. We compare model predictions with photometric and spectroscopic observations of the star, aiming to reach a self-consistency between the abundance pattern derived from high-resolution spectra and abundances used for model atmosphere calculation. Based on magnetic model atmospheres, we redetermined abundances and fundamental parameters of HD137509 using spectroscopic and photometric observations. This allowed us to obtain a better agreement between observed and theoretical parameters compared to non-magnetic models with individual or scaled-solar abundances. We confirm that the magnetic field effects should be taken into account in the stellar parameter determination and abundance analysis.
