EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 499/3 Article
Free access article

Issue A&A
Volume 499, Number 3, June I 2009
Page(s) 851 - 863
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361/200911653
Published online 08 April 2009

A&A 499, 851-863 (2009)
DOI: 10.1051/0004-6361/200911653

A self-consistent empirical model atmosphere, abundance and stratification analysis of the benchmark roAp star $\alpha$ Circini

O. Kochukhov1, D. Shulyak2, and T. Ryabchikova2, 3

1  Department of Physics and Astronomy, Uppsala University, Box 515, 751 20 Uppsala, Sweden
    e-mail: oleg@fysast.uu.se
2  Institute of Astronomy, Vienna University, Turkenschanzstrasse 17, 1180 Vienna, Austria
3  Institute of Astronomy, Russian Academy of Science, Pyatnitskaya 48, 119017 Moscow, Russia

Received 13 January 2009 / Accepted 15 March 2009

Abstract
Context. Chemically peculiar (CP) stars are unique natural laboratories for the investigation of the microscopic diffusion processes of chemical elements. The element segregation under the influence of gravity and radiation pressure leads to the appearance of strong abundance gradients in the atmospheres of CP stars. Consequently, the atmospheric temperature-pressure structure of these objects could deviate significantly from the atmospheres of normal stars with homogeneous abundances.
Aims. In this study we performed a self-consistent, empirical model atmosphere study of the brightest rapidly oscillating Ap star $\alpha$ Cir. We account for chemical stratification in the model atmosphere calculations and assess the importance of non-uniform vertical element distribution on the model structure, energy distribution and hydrogen line profiles.
Methods. For the chemical stratification analysis we use the DDAFIT minimization tool in combination with a magnetic spectrum synthesis code. The model atmospheres with inhomogeneous vertical distributions of elements are calculated with the LLMODELS stellar model atmosphere code.
Results. Based on an iterative procedure of the chemical abundance analysis of 52 ions of 35 elements, stratification modeling of 4 elements (Si, Ca, Cr and Fe) and subsequent re-calculations of the atmospheric structure, we derived a new model atmosphere of $\alpha$ Cir which is consistent with the inferred atmospheric chemistry of the star. We find $T_{\rm eff}$ = 7500 K, log g = 4.1, and demonstrate that chemical stratification has a noticeable impact on the model structure and modifies the formation of the hydrogen Balmer lines. At the same time, the energy distribution appears to be less sensitive to the presence of large abundance gradients.
Conclusions. Our spectroscopically determined $T_{\rm eff}$ of $\alpha$ Cir agrees with the fundamental effective temperature of this star. This shows that temperatures inferred in detailed spectroscopic analyses of cool magnetic CP stars are not affected by a large systematic bias.


Key words: stars: abundances -- stars: atmospheres -- stars: chemically peculiar -- stars: individual: $\alpha$ Circini



© ESO 2009


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.