Morphology and kinematics of the gas envelope of the Mira binary W Aquilae

TL;DR

This study presents spatially resolved ALMA observations of W Aql's circumstellar envelope, revealing its morphology and kinematics, with emission enhancements and velocity asymmetries indicating complex gas dynamics around the binary star.

Contribution

First spatially resolved Doppler velocity spectra of W Aql's CSE, providing qualitative insights into its morphology and kinematics from ALMA data.

Findings

Emission enhancement along a specific axis with increasing distance from the star.

Asymmetry in Doppler velocity distribution along a different axis.

Qualitative evidence of complex gas dynamics in the circumstellar envelope.

Abstract

We analyse ALMA observations of the 12CO(3-2) emission of the circumstellar envelope (CSE) of the Mira variable binary star W Aql. These provide, for the first time, spatially resolved Doppler velocity spectra of the CSE up to angular distances to the central star of ~ 5" (meaning some 2000 AU). The exploratory nature of the observations (only five minutes in each of two different configurations) does not allow for a detailed modelling of the properties of the CSE but provides important qualitative information on its morphology and kinematics. Emission is found to be enhanced along an axis moving from east/west to north-east/south-west when the angular distance from the central star projected on the plane of the sky increases from zero to four arcseconds. In parallel, the Doppler velocity distribution displays asymmetry along an axis moving from east/west to north-west/south-east. The results are discussed in the context of earlier observations, in particular of the dust morphology.