243 research outputs found
Abundance and stratification analysis of the CP star HD 103498
Slow rotation and absence of strong mixing processes in atmospheres of
chemically peculiar stars develop ideal conditions for the appearance of
abundance anomalies through the mechanism of microscopic particle diffusion.
This makes these objects look spectroscopically and photometrically different
from their "normal" analogs. As a result, it is often difficult to accurately
determine atmospheric parameters of these stars and special methods are needed
for the consistent analysis of their atmospheres. The main aim of the present
paper is to analyse atmospheric abundance and stratification of chemical
elements in the atmosphere of the chemically peculiar star HD 103498. We find
that two model atmospheres computed with individual and stratified abundances
provide reasonable fit to observed spectroscopic and photometric indicators:
Teff=9300 K, logg=3.5 and Teff=9500K, logg=3.6. It is shown that Mg has a large
abundance gradient in the star's atmosphere with accumulation of Mg ions in the
uppermost atmospheric layers, whereas Si demonstrates opposite behaviour with
accumulation in deep layers. In addition, a detailed non-LTE analysis showed
that none of Mg transitions under consideration is a subject of noticeable
non-LTE effects. Comparing observed photometry transformed to physical units we
estimated the radius of HD 103498 to be between R=(4.56 +/- 0.77)Rsun for
Teff=9300K, logg=3.5 and R=(4.39 +/- 0.75)Rsun for Teff=9500K, logg=3.6 models
respectively. We note that the lack of suitable observations in absolute units
prevents us to uniquely determine the Teff of the star at the current stage of
analysis.Comment: 9 pages, 7 figures and 3 tables, accepted for publication in MNRA
Pushing the limit of instrument capabilities
Chemically Peculiar (CP) stars have been subject of systematic research since
more than 50 years. With the discovery of pulsation of some of the cool CP
stars, the availability of advanced spectropolarimetric instrumentation and
high signal- to-noise, high resolution spectroscopy, a new era of CP star
research emerged about 20 years ago. Together with the success in ground-based
observations, new space projects are developed that will greatly benefit for
future investigations of these unique objects. In this contribution we will
give an overview of some interesting results obtained recently from
ground-based observations and discuss on future outstanding Gaia space mission
and its impact on CP star research.Comment: Joint Discussion 04, Secsion 1, To appear in Highlights of Astronomy,
Proc. of the XXVIIth IAU General Assembly, Rio de Janeiro, Brazil, August
2009, 9 page
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&
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.Comment: Accepted by A&A; 12 pages, 9 figure
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