The wonderful complexity of the Mira AB system

TL;DR

This study uses high-resolution ALMA observations to reveal the complex gas morphology around Mira AB, including spiral structures, an accretion wake, and large arcs, illustrating dynamic interactions in the system.

Contribution

First detailed ALMA CO(3-2) mapping of Mira AB revealing complex gas structures and dynamical interactions in the system.

Findings

Identification of spiral arcs around Mira A.

Detection of an accretion wake behind Mira B.

Observation of large opposing arcs possibly caused by Mira B's wind.

Abstract

We have mapped the CO(3-2) line emission around the Mira AB system at 0.5 resolution using the Atacama Large Millimeter/submillimeter Array (ALMA). The CO map shows amazing complexity. The circumstellar gas has been shaped by different dynamical actors during the evolution of the system and several morphological components can be identified. The companion is marginally resolved in continuum emission and is currently at 0.487$\pm$0.006 separation. In the main line component, centered on the stellar velocity, spiral arcs around Mira A are found. The spiral appears to be relatively flat and oriented in the orbital plane. An accretion wake behind the companion is clearly visible and the projected arc separation is of order 5''. In the blue wing of the line emission, offset from the main line, several large ($\sim$5-10''), opposing arcs are found. We tentatively suggest that this structure is created by the wind of Mira B blowing a bubble in the expanding envelope of Mira A.