The Lorentz force in atmospheres of chemically peculiar stars: 56 Arietis

D. Shulyak¹, O. Kochukhov², G. Valyavin³, B.-C. Lee⁴, G. Galazutdinov⁵, K.-M. Kim⁴, I. Han⁴ and T. Burlakova⁶

¹ Institut für Astronomie, Universität Wien, Türkenschanzstraße 17, 1180 Wien, Austria e-mail: denis.shulyak@gmail.com
² Department of Physics and Astronomy, Uppsala University, Box 515, 751 20, Uppsala, Sweden
³ Observatorio Astronómico Nacional SPM, Instituto de Astronomía, Universidad Nacional Autónoma de México, Ensenada, BC, México
⁴ Korea Astronomy and Space Science Institute, 61-1, Whaam-Dong, Youseong-Gu, Taejeon, 305-348, Rep. of Korea
⁵ Department of Physics and Astronomy, Seoul National University, Gwanak-gu, Seoul 151-747, Rep. of Korea
⁶ Special Astrophysical Observatory, Russian Academy of Sciences, Nizhnii Arkhyz, Karachai Cherkess Republic, 369167, Russia

Received: 2 June 2009
Accepted: 1 October 2009

Abstract

Context. The presence of electric currents in the atmospheres of magnetic chemically peculiar (mCP) stars could theoretically constrain the nature and evolution of magnetic field in these stars. The Lorentz force, which is the result of the interaction between the magnetic field and the induced currents, modifies the atmospheric structure and induces characteristic rotational variability of pressure-sensitive spectroscopic features, which can be analyzed using phase-resolved spectroscopic observations.

Aims. In this work we continue presenting the results of the magnetic pressure studies in mCP stars focusing on the high-resolution spectroscopic observations of Bp star 56 Ari.

Methods. We interpreted observations in the framework of the model atmosphere analyzis, which accounts for the Lorentz force effects. We used the llmodels stellar model atmosphere code for the calculation of the magnetic pressure effects in the atmosphere of 56 Ari  by taking the realistic chemistry of the star and accurate computations of the microscopic plasma properties into account. The synth3 code was employed to simulate phase-resolved variability of Balmer lines.

Results. We detected a significant variability of the Hα, Hβ, and Hγ spectral lines during a full rotation cycle of the star. We demonstrate that the model with the outward-directed Lorentz force in the dipole+quadrupole configuration is likely to reproduce the observed hydrogen lines variation. These results present strong evidence of non-zero global electric currents in the atmosphere of this early-type magnetic star.