Multi-epoch imaging polarimetry of the SiO masers in the extended atmosphere of the Mira variable TX Cam

TL;DR

This paper presents a detailed time series of polarized SiO maser images around TX Cam, revealing polarization patterns and dynamics that inform understanding of magnetic fields in evolved star atmospheres.

Contribution

It provides the first synoptic polarization image sequence of SiO masers in TX Cam, highlighting polarization morphology and potential magnetic influences over multiple epochs.

Findings

Predominantly tangential polarization morphology.

High persistence of polarization properties over component lifetimes.

Stronger polarization in inner shell regions.

Abstract

We present a time series of synoptic images of the linearly-polarized v=1, J=1-0 SiO maser emission toward the Mira variable, TX Cam. These data comprise 43 individual epochs at an approximate biweekly sampling over an optical pulsation phase range of 0.68 to 1.82. The images have an angular resolution of ~500 microarcsec and were obtained using the Very Long Baseline Array (VLBA), operating in the 43 GHz band in spectral-line, polarization mode. We have previously published the total intensity time series for this pulsation phase range; this paper serves to present the linearly-polarized image sequence and an associated animation representing the evolution of the linear polarization morphology over time. We find a predominantly tangential polarization morphology, a high degree of persistence in linear polarization properties over individual component lifetimes, and stronger linear polarization in the inner projected shell than at larger projected shell radii. We present an initial polarization proper motion analysis examining the possible dynamical influence of magnetic fields in component motions in the extended atmospheres of late-type, evolved stars.