Model atmospheres of magnetic chemically peculiar stars

A remarkable strong-field Bp SiCrFe star HD 137509

¹ Institute of Astronomy, Vienna University, Turkenschanzstrasse 17, 1180 Vienna, Austria e-mail: denis@jan.astro.univie.ac.at
² Department of Astronomy and Space Physics, Uppsala University, Box 515, 751 20, Uppsala, Sweden
³ Physics and Astronomy Department, University of Western Ontario, London, ON, N6A 3K7, Canada
⁴ Institute for Computational Astrophysics, Saint Mary's University, 923 Robie Street, Halifax, B3H 3C3, Nova Scotia, Canada

Received: 23 November 2007
Accepted: 19 May 2008

Abstract

Context. In the past few years, we have developed stellar model atmospheres that included effects of anomalous abundances and a strong magnetic field. In particular, the full treatment of anomalous Zeeman splitting and polarized radiative transfer were introduced in the model atmosphere calculations for the first time. The influence of the magnetic field on the model atmosphere structure and various observables were investigated for stars of different fundamental parameters and metallicities. However, these studies were purely theoretical and did not attempt to model real objects.

Aims. In this investigation we present results of modeling the atmosphere of one of the most extreme magnetic chemically peculiar stars, HD 137509. This Bp SiCrFe star has a mean surface magnetic field modulus of about 29 kG. Such a strong field, as well as clearly observed abundance peculiarities, make this star an interesting target for applying our newly developed model atmosphere code.

Methods. We used 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 compared model predictions with photometric and spectroscopic observations of HD 137509, aiming to reach a self-consistency between the abundance pattern derived from high-resolution spectra and abundances used for model atmosphere calculation.

Results. Based on magnetic model atmospheres, we redetermined abundances and fundamental parameters of HD 137509 using spectroscopic and photometric observations. This allowed us to obtain better agreement between observed and theoretical parameters compared to non-magnetic models with individual or scaled-solar abundances.

Conclusions. We confirm that the magnetic field effects lead to noticeable changes in the model atmosphere structure and should be taken into account in the stellar parameter determination and abundance analysis.