Measuring the surface magnetic fields of magnetic stars with unresolved Zeeman splitting

TL;DR

This paper develops a simple, reliable method to estimate the mean surface magnetic fields of Ap stars with unresolved Zeeman splitting, especially for stars with high rotational velocities, improving magnetic field measurements.

Contribution

It introduces a new relation based on spectral line broadening to estimate magnetic fields in stars with unresolved Zeeman patterns, extending measurement capabilities.

Findings

Method is reliable for v sin i up to 50 km/s.

Can estimate magnetic fields down to about 5 kG.

Improves constraints on magnetic field measurements in Ap stars.

Abstract

High-dispersion, archival spectra of magnetic Ap stars with resolved Zeeman components in Stokes I are used to derive a simple relation that can be utilised to estimate the mean surface field strengths of stars with v sin i > 10 km/s. For each star, the mean surface field, as measured from the observed splitting in Fe II at 6149 A, is compared to the differential broadening of spectral lines with large and small Lande factors in order to produce a relation to estimate the field strengths of magnetic stars with unresolved Zeeman patterns. The method is shown to be reliable for rotational velocities up to about 50 km/s for field strengths down to about 5 kG. These results should allow for better constraints to be placed on the mean surface magnetic fields of Ap stars where Zeeman patterns are unresolved.