The Zeeman Effect in the Sobolev Approximation II: Split Monopole Fields and the "Heartbeat" Stokes V Profile

TL;DR

This paper models the circular polarization (Stokes V) profiles in hot-star winds with radial magnetic fields, revealing a characteristic heartbeat shape with multiple sign inversions that could be mistaken for noise.

Contribution

It introduces a theoretical calculation of Stokes V profiles for split monopole magnetic fields in stellar winds, highlighting the heartbeat shape and zero-integral tendency.

Findings

V profile exhibits multiple sign inversions

Profiles tend to integrate to zero on each side of the line

Heartbeat shape can be mistaken for noise

Abstract

We calculate the circularly polarized Stokes V profile for emission lines, formed in hot-star winds threaded with a weak radial magnetic field. For simplicity, the field is treated as a split monopole under the assumptions that it has been radially combed by the wind, and rotation is not playing a central role. Invoking the weak-field approximation, we find that the V profile has a characteristic ``heartbeat'' shape exhibiting multiple sign inversions, which might be mistaken for noise in the absence of theoretical guidance. We also conclude that there is a tendency for the V profile to integrate to zero on each side of the line separately.