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

摘要

High-dispersion, archival spectra of magnetic Ap stars with resolved Zeemancomponents in Stokes I are used to derive a simple relation that can beutilised 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 observedsplitting in Fe II at 6149 A, is compared to the differential broadening ofspectral lines with large and small Lande factors in order to produce arelation to estimate the field strengths of magnetic stars with unresolvedZeeman patterns. The method is shown to be reliable for rotational velocities up to about 50km/s for field strengths down to about 5 kG. These results should allow for better constraints to be placed on the meansurface magnetic fields of Ap stars where Zeeman patterns are unresolved.