arXiv subjects

V. Tsymbal

Publications and source records attributed to V. Tsymbal.

23 records · Page 2Linked to original sources

arXiv2006

The Lorentz force in atmospheres of CP stars: $θ$ Aurigae

Several dynamical processes may induce considerable electric currents in the atmospheres of magnetic chemically peculiar (CP) stars. The Lorentz force, which results from the interaction between the magnetic field and the induced currents, modifies the atmospheric structure and induces characteristic rotational variability of the hydrogen Balmer lines. To study this phenomena we have initiated a systematic spectroscopic survey of the Balmer lines variation in magnetic CP stars. In this paper we continue presentation of results of the program focusing on the high-resolution spectral observations of A0p star \aur (HD 40312). We have detected a significant variability of the H$α$, H$β$, and H$γ$ spectral lines during full rotation cycle of the star. This variability is interpreted in the framework of the model atmosphere analysis, which accounts for the Lorentz force effects. Both the inward and outward directed Lorentz forces are considered under the assumption of the axisymmetric dipole or dipole+quadrupole magnetic field configurations. We demonstrate that only the model with the outward directed Lorentz force in the dipole+quadrupole configuration is able to reproduce the observed hydrogen line variation. These results present new strong evidences for the presence of non-zero global electric currents in the atmosphere of an early-type magnetic star.

astro-ph↗

arXiv2006

Chemical stratification in the atmosphere of Ap star HD 133792. Regularized solution of the vertical inversion problem

High spectral resolution studies of cool Ap stars reveal conspicuous anomalies of the shape and strength of many absorption lines. This is a signature of large atmospheric chemical gradients produced by the selective radiative levitation and gravitational settling of chemical species. Here we present a new approach to mapping the vertical chemical structures in stellar atmospheres. We have developed a regularized chemical inversion procedure that uses all information available in high-resolution stellar spectra. The new technique for the first time allowed us to recover chemical profiles without making a priori assumptions about the shape of chemical distributions. We have derived average abundances and applied the vertical inversion procedure to the high-resolution VLT UVES spectra of the weakly magnetic, cool Ap star HD 133792. Our analysis yielded improved estimates of the atmospheric parameters of HD 133792. We show that this star has negligible vsini and the mean magnetic field modulus =1.1+/-0.1 kG. We have derived average abundances for 43 ions and obtained vertical distributions of Ca, Si, Mg, Fe, Cr, and Sr. All these elements except Mg show high overabundance in the deep layers and solar or sub-solar composition in the upper atmosphere of HD 133792. In contrast, the Mg abundance increases with height. We find that transition from the metal-enhanced to metal-depleted zones typically occurs in a rather narrow range of depths in the atmosphere of HD 133792. Based on the derived photospheric abundances, we conclude that HD 133792 belongs to the rare group of evolved cool Ap stars, which possesses very large Fe-peak enhancement, but lacks a prominent overabundance of the rare-earth elements.

astro-ph↗

arXiv2005

Prospects for population synthesis in the H band: NeMo grids of stellar atmospheres compared to observations

For applications in population synthesis, libraries of theoretical stellar spectra are often considered an alternative to template libraries of observed spectra, because they allow a complete sampling of stellar parameters. Most attention in published theoretical spectral libraries has been devoted to the visual wavelength range. We present a detailed comparison of theoretical spectra in the range 1.57-1.67$μ$m, for spectral types from A to early M and for giants and dwarf stars, with observed stellar spectra at resolutions around 3000, which would be sufficient to disentangle the different groups of late type stars. We have selected the NeMo grids of stellar atmospheres to perform such a comparison. We first demonstrate that after combining atomic and molecular line lists, it is possible to match observed spectral flux distributions with theoretical ones very well for almost the entire parameter range covered by the NeMo grids at moderate resolution in the visual range. In the infrared range, although the overall shape of the observed flux distributions is still matched reasonably well, the individual spectral features are reproduced by the theoretical spectra only for stars earlier than mid F type. For later spectral types the differences increase and theoretical spectra of K type stars have systematically weaker line features than those found in observations. These discrepancies are traced back to stem primarily from incomplete data on neutral atomic lines, although some of them are also related to molecules. Improving atomic data in the near infrared is a key element in making the construction of reliable libraries of stellar spectra in the infrared feasible.

astro-ph↗

arXiv2004

GAUDI: a preparatory archive for the COROT mission

The GAUDI database (Ground-based Asteroseismology Uniform Database Interface, http://sdc.laeff.esa.es/gaudi/) is a preparatory archive for the COROT (COnvection, ROtation and planetary Transits, http://www.astrsp-mrs.fr/projets/corot/) mission developed at LAEFF (Laboratory for Space Astrophysics and Theoretical Physics, http://www.laeff.esa.es). Its intention is to make the ground-based observations obtained in the preparation of the asteroseismology programme available in a simple and efficient way. It contains spectroscopic and photometric data together with inferred physical parameters for more than 1500 objects gathered since January 1998 in 6 years of observational campaigns. In this paper, the main functionalities and characteristics of the system are described. The observations have been collected at ESO-La Silla, Telescopio Nazionale Galileo, Observatoire de Haute-Provence, South African Astronomical Observatory, Tautenberg Observatory and Sierra Nevada Observatory.

astro-ph↗

arXiv2003

On the influence of Stark broadening on Si I lines in stellar atmospheres

We study the influence of Stark broadening and stratification effects on Siılines in the rapidly oscillating (roAp) star 10 Aql, where the Siı6142.48 Åand 6155.13 Ålines are asymmetrical and shifted. First we have calculated Stark broadening parameters using the semiclassical perturbation method for three Siılines: 5950.2 Å, 6142.48 Åand 6155.13 Å. We revised the synthetic sp$ calculation code taking into account both Stark width and shift for these lines. From the comparison of our calculations with the observations we found that Stark broadening + the stratification effect can explain asymmetry of the Siı6142.48 Åand 6155.13 Ålines in the atmospere of roAp star 10 Aql.

astro-ph↗