The Lorentz force in atmospheres of CP stars: 56 Arietis

TL;DR

This study investigates the impact of the Lorentz force caused by electric currents on the atmospheres of magnetic chemically peculiar stars, using high-resolution spectroscopy of 56 Arietis to detect and model spectral line variability.

Contribution

It provides the first detailed modeling of Lorentz force effects on Balmer line variability in 56 Arietis, confirming the presence of global electric currents in its atmosphere.

Findings

Detected significant spectral line variability during star rotation.

Model with outward Lorentz force reproduces observed line variations.

Evidence for non-zero electric currents in the star's atmosphere.

Abstract

The presence of electric currents in the atmospheres of magnetic chemically peculiar (mCP) stars could bring important theoretical constrains about the nature and evolution of magnetic field in these stars. The Lorentz force, which results from the interaction between the magnetic field and the induced currents, modifies the atmospheric structure and induces characteristic rotational variability of pressure-sensitive spectroscopic features, that can be analysed using phase-resolved spectroscopic observations. In this work we continue the presentation of results of the magnetic pressure studies in mCP stars focusing on the high-resolution spectroscopic observations of Bp star 56Ari. We have detected a significant variability of the Halpha, Hbeta, and Hgamma spectral lines during full rotation cycle of the star. Then these observations are interpreted in the framework of the model atmosphere analysis, 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 56Ari taking into account realistic chemistry of the star and accurate computations of the microscopic plasma properties. The Synth3 code was employed to simulate phase-resolved variability of Balmer lines. 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 evidences for the presence of non-zero global electric currents in the atmosphere of this early-type magnetic star.