Model atmospheres of magnetic chemically peculiar stars - A remarkable strong-field Bp SiCrFe star HD 137509

Context. In the last few years we have developed stellar model atmospheres which included effects of anomalous abundances and strong magnetic field. In particular, the full treatment of a nomalous Zeeman splitting and polarized radiative transfer were introduced in the model atmosphere calculations for the first time. The i nfluence of the magnetic field on the model atmosphere structu re 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 modelling the at mosphere of one of the most extreme magnetic chemically peculiar stars, HD 137509. This Bp SiCrFe star has the mean surface magnetic field modulus of about 29 kG. Such a strong field, as well a s clearly observed abundance peculiarities, make this star an interesting target for application of our newly developed model atmosphere code. Methods. We use 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, de tailed polarized radiative transfer and arbitrary abundan ces. We compare 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 a 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 e ffects lead to noticeable changes in the model atmosphere structure and should be taken into account in the stellar parameter determination and abundance analysis.

[1]  Evolutionary state of magnetic chemically peculiar stars , 2006, astro-ph/0601461.

[2]  H. C. Stempels,et al.  VALD{2: Progress of the Vienna Atomic Line Data Base ? , 1999 .

[3]  O. Kochukhov,et al.  Stellar model atmospheres with magnetic line blanketing , 2007 .

[4]  T. Sigut,et al.  Magnetic Doppler imaging of 53 Camelopardalis in all four Stokes parameters , 2004 .

[5]  C. Ledoux,et al.  The UVES Paranal Observatory Project: A Library of High- Resolution Spectra of Stars across the Hertzsprung-Russell Diagram , 2003 .

[6]  D. V. Shulyak,et al.  Stellar model atmospheres with magnetic line blanketing III. The role of magnetic field inclination , 2006 .

[7]  D. Shulyak,et al.  Stellar model atmospheres with magnetic line blanketing II. Introduction of polarized radiative transfer , 2005, astro-ph/0511744.

[8]  M. Dworetsky,et al.  Peculiar versus Normal Phenomena in A-type and Related Stars , 1993 .

[9]  F. V. Leeuwen,et al.  Hipparcos, the New Reduction of the Raw Data , 2007 .

[10]  B.-C. Lee,et al.  The Lorentz force in atmospheres of CP stars: θ Aurigae , 2007 .

[11]  O. Kochukhov,et al.  Chemical stratification in the atmosphere of Ap star HD 133792. Regularized solution of the vertical inversion problem , 2006, astro-ph/0609312.

[12]  Remarkable non-dipolar magnetic field of the Bp star HD 137509 , 2006, astro-ph/0603831.

[13]  D. Shulyak,et al.  Theoretical analysis of the atmospheres of CP stars - Effects of the individual abundance patterns , 2007, 0706.4028.

[14]  M. Mermilliod,et al.  $uvby\beta$ photoelectric photometric catalogue , 1998 .

[15]  Werner W. Weiss,et al.  Line-by-line opacity stellar model atmospheres , 2004 .

[16]  G. Alecian,et al.  Modelling element distributions in the atmospheres of magnetic Ap stars , 2007, 0711.1076.