H2O Maser Polarization of the Water Fountains IRAS 15445-5449 and IRAS 18043-2116

TL;DR

This study investigates the morphology and polarization of 22-GHz H2O masers in the high-velocity outflows of two post-AGB stars, revealing magnetic field structures and their potential role in jet dynamics.

Contribution

First detailed polarization analysis of H2O masers in these post-AGB sources, linking maser polarization to magnetic field geometry and jet activity.

Findings

Detected different saturation levels of maser emission.

Polarization vectors trace magnetic field components.

Estimated upper limits on magnetic field strength.

Abstract

We present the morphology and linear polarization of the 22-GHz H2O masers in the high-velocity outflow of two post-AGB sources, d46 (IRAS 15445-5449) and b292 (IRAS 18043-2116). The observations were performed using The Australia Telescope Compact Array. Different levels of saturated maser emission have been detected for both sources. We also present the mid-infrared image of d46 overlaid with the distribution of the maser features that we have observed in the red-shifted lobe of the bipolar structure. The relative position of the observed masers and a previous radio continuum observation suggests that the continnum is produced along the blue-shifted lobe of the jet. It is likely due to synchrontron radiation, implying the presence of a strong magnetic field in the jet. The fractional polarization levels measured for the maser features of d46 indicate that the polarization vectors are tracing the poloidal component of the magnetic field in the emitting region. For the H2O masers of b292 we have measured low levels of fractional linear polarization. The linear polarization in the H2O maser region of this source likely indicates a dominant toroidal or poloidal magnetic field component. Since circular polarization was not detected it is not possible to determine the magnetic field strength. However, we present a 3-sigma evaluation of the upper limit intensity of the magnetic field in the maser emitting regions of both observed sources.