Physical variability of the magnetic field of some stars

TL;DR

This paper investigates the apparent variability of stellar magnetic fields caused by rotation and observes faster-than-expected changes in magnetic phase curves, indicating a need to improve magnetic field evolution theories.

Contribution

It demonstrates observed changes in magnetic phase curves in stars, highlighting discrepancies with existing theoretical predictions.

Findings

Magnetic phase curves change over several years in some stars.

Variability is mainly due to geometric effects of rotation.

Observed changes are faster than current theories predict.

Abstract

Apparent variability of the longitudinal magnetic fields in most stars is caused by rotation, which quantitavely changes projection of the magnetic field configuration on the line of sight. This is a purely geometrical effect and is not related to possible intrinsic changes of the field. In some stars we observe changes of the magnetic phase curve with time, which means that parameters of the magnetic field change. Such changes occur in some objects in time scale of several years, which is few orders of magnitude faster than predicted by theory. Those changes imply need for improvement of the theory of magnetic field evolution. We demonstrate changes of the rotational phase curves in few stars.