Multiline Zeeman signatures as demonstrated through the Pseudo-line

TL;DR

This paper clarifies the interpretation of multiline Zeeman signatures in stellar spectra, demonstrating that the pseudo-line approach effectively detects magnetic fields in stars, extending the applicability of solar magnetism methods.

Contribution

It provides a theoretical and practical validation of the pseudo-line technique for detecting stellar magnetic fields using standard solar methods.

Findings

Zeeman signatures are reliably detected in synthetic multiline spectra.

Solar magnetism methods are effective for stellar observations.

Magnetic field measurements are reliable beyond the weak-field approximation.

Abstract

In order to get a significant Zeeman signature in the polarised spectra of a magnetic star, we usually 'add' the contributions of numerous spectral lines; the ultimate goal is to recover the spectropolarimetric prints of the magnetic field in these line additions. Here we want to clarify the meaning of these techniques of line addition; in particular, we try to interpret the meaning of the 'pseudo-line' formed during this process and to find out why and how its Zeeman signature is still meaningful. We create a synthetic case of lines addition and apply well tested standard solar methods routinely used in the research on magnetism in our nearest star. The results are convincing and the Zeeman signatures well detected; Solar methods are found to be quite efficient also for stellar observations. The Zeeman signatures are unequivocally detected in this multiline approach. We may anticipate the outcome magnetic fields to be reliable well beyond the weak-field approximation. Linear polarisation in the spectra of solar type stars can be detected when the spectral resolution is sufficiently high.