The rapidly oscillating Ap star gamma Equ: linear polarization as an enhanced pulsation diagnostic?

TL;DR

This study uses linear polarization observations of the roAp star gamma Equ to explore pulsation effects on magnetic field components, revealing potential pulsation-induced magnetic variability and highlighting the need for further detailed modeling.

Contribution

First short time scale linear polarization observations of gamma Equ, demonstrating potential pulsation effects on the transverse magnetic field component.

Findings

Detection of variability in the transverse magnetic field in certain spectral lines.

Possible pulsation impact on magnetic obliquity angles.

Indication that linear polarization can serve as an enhanced pulsation diagnostic.

Abstract

We present the first short time scale observations of the roAp star gamma Equ in linear polarized light obtained with the PEPSI polarimeter installed at the LBT. These observations are used to search for pulsation variability in Stokes Q and U line profiles belonging to different elements. The atmospheres of roAp stars are significantly stratified with spectral lines of different elements probing different atmospheric depths. roAp stars with strong magnetic fields, such as gamma Equ with a magnetic field modulus of 4kG and a pulsation period of 12.21min, are of special interest because the effect of the magnetic field on the structure of their atmospheres can be studied with greatest detail and accuracy. Our results show that we may detect changes in the transversal field component in Fe I and rare-earth lines possessing large second-order Lande factors. Such variability can be due to the impact of pulsation on the transverse magnetic field, causing changes in the obliquity angles of the magnetic force lines. Further studies of roAp stars in linear polarized light and subsequent detailed modelling are necessary to improve our understanding of the involved physics.