Zeeman split lines in CP stars: a discovery of low-contrast fields in slow rotators?

Abstract

We show that high-resolution observations of resolved Zeeman split lines can be used to obtain new constraints on the stellar magnetic field geometry. In particular, the contrast of the field strength distribution over the stellar surface can be deduced from the differential measurement of the second moment of the pi and sigma Zeeman components. Our analysis of the triplet lines in slowly rotating cool magnetic CP stars uncovers a surprisingly homogeneous field structure, inconsistent with any low-order multipolar geometry.