Partial Paschen-Back splitting of silicon lines in magnetic CP stars

TL;DR

This paper investigates the partial Paschen-Back effect on silicon spectral lines in magnetic chemically peculiar stars, demonstrating that for strong magnetic fields, PPB modeling yields more accurate spectral line profiles than Zeeman approximation.

Contribution

It introduces the importance of using the PPB effect for modeling silicon lines in strong magnetic fields, improving spectral analysis accuracy in magnetic CP stars.

Findings

PPB effect significantly alters spectral line profiles at Bp > 6-10 kG.

PPB modeling provides better fits to observed spectra than Zeeman approximation.

Ghost lines contribute notably to the spectral features in the PPB regime.

Abstract

A number of prominent spectral lines in the spectra of magnetic A and B main sequence stars are produced by closely spaced doublets or triplets. Depending on the strength and orientation of magnetic field, the PPB magnetic splitting can result in the Stokes $I$ profiles of a spectral line that differ significantly from those predicted by the theory of Zeeman effect. Such lines should be treated using the theory of the partial Paschen-Back (PPB) effect. To estimate the error introduced by the use of the Zeeman approximation, numerical simulations have been performed for Si II and Si III lines assuming an oblique rotator model. The analysis indicates that for high precision studies of some spectral lines the PPB approach should be used if the field strength at the magnetic poles is Bp> 6-10 kG and Vsin(i) < 15 km/s. In the case of the Si II line 5041A the difference between the simulated PPB and Zeeman profiles is caused by a significant contribution from a so called "ghost" line. The Stokes I and V profiles of this particular line simulated in the PPB regime provide a significantly better fit to the observed profiles in the spectrum of the magnetic Ap star HD318107 than the profiles calculated assuming the Zeeman effect.