78 research outputs found
Stellar model atmospheres with magnetic line blanketing. II. Introduction of polarized radiative transfer
The technique of model atmosphere calculation for magnetic Ap and Bp stars
with polarized radiative transfer and magnetic line blanketing is presented. A
grid of model atmospheres of A and B stars are computed. These calculations are
based on direct treatment of the opacities due to the bound-bound transitions
that ensures an accurate and detailed description of the line absorption and
anomalous Zeeman splitting. The set of model atmospheres was calculated for the
field strengths between 1 and 40 kG. The high-resolution energy distribution,
photometric colors and the hydrogen Balmer line profiles are computed for
magnetic stars with different metallicities and are compared to those of
non-magnetic reference models and to the previous paper of this series. The
results of modelling confirmed the main outcomes of the previous study: energy
redistribution from UV to the visual region and flux depression at 5200A.
However, we found that effects of enhanced line blanketing when transfer for
polarized radiation takes place are smaller in comparison to those obtained in
our first paper where polarized radiative transfer was neglected. Also we found
that the peculiar photometric parameter delta_a is not able to clearly
distinguish stellar atmospheres with abundances other than solar, and is less
sensitive than delta(V_1-G) or Z to a magnetic field for low effective
temperature (Teff=8000K). Moreover we found that the back determination of the
fundamental stellar atmosphere parameters using synthetic Stromgren photometry
does not result in significant errors.Comment: 12 pages, 6 figures. The final version, Sect. 3.4 revised, typos and
mistakes correcte
The Lorentz force in atmospheres of CP stars: 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,
H, and H 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.Comment: 10 figure
Exergic balance and efficiency of reverse osmosis modules
In this paper the option of using exergy analysis method is proposed for preparing make-up water by reverse osmosis systems (ROS), which are spreading in the reconstruction of the chemical departments of Ukrainian nuclear power plants. The estimation of exergy efficiency of water purification by membrane units is made and the nature of influence of the ROS main parameters on thermodynamic efficiency is identified. The conclusion on the possible ways of facilities improvement is drawn
An In-Depth Spectroscopic Analysis of the Blazhko Star RR Lyr. I. Characterisation of the star: abundance analysis and fundamental parameters
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.Comment: 12 pages, accepted for publication in Astronomy & Astrophysic
Spectral analysis of Kepler SPB and Beta Cep candidate stars
We determine the fundamental parameters of SPB and Beta Cep candidate stars
observed by the Kepler satellite mission and estimate the expected types of
non-radial pulsators by comparing newly obtained high-resolution spectra with
synthetic spectra computed on a grid of stellar parameters assuming LTE and
check for NLTE effects for the hottest stars. For comparison, we determine Teff
independently from fitting the spectral energy distribution of the stars
obtained from the available photometry. We determine Teff, log(g),
micro-turbulent velocity, vsin(i), metallicity, and elemental abundance for 14
of the 16 candidate stars, two of the stars are spectroscopic binaries. No
significant influence of NLTE effects on the results could be found. For hot
stars, we find systematic deviations of the determined effective temperatures
from those given in the Kepler Input Catalogue. The deviations are confirmed by
the results obtained from ground-based photometry. Five stars show reduced
metallicity, two stars are He-strong, one is He-weak, and one is Si-strong. Two
of the stars could be Beta Cep/SPB hybrid pulsators, four SPB pulsators, and
five more stars are located close to the borders of the SPB instability region.Comment: 10 pages, 10 figures, 10 table
On the influence of Stark broadening on Si I lines in stellar atmospheres
We study the influence of Stark broadening and stratification effects on Si\i
lines in the rapidly oscillating (roAp) star 10 Aql, where the Si\i 6142.48 \AA
and 6155.13 \AA lines are asymmetrical and shifted. First we have calculated
Stark broadening parameters using the semiclassical perturbation method for
three Si\i lines: 5950.2 \AA, 6142.48 \AA and 6155.13 \AA. 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 Si\i 6142.48 \AA and 6155.13 \AA lines in the atmospere of
roAp star 10 Aql.Comment: Accepted to A&
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