It's a wonderful tail: the mass loss history of Mira

TL;DR

This study models the bow shock and tail of Mira as an interaction between its stellar wind and the interstellar medium, revealing turbulence, age, and possible recent entry into the Local Bubble, with implications for mass-loss history.

Contribution

The paper provides hydrodynamic simulations of Mira's bow shock and tail, offering new insights into their structure, turbulence, age, and the star's recent environmental changes.

Findings

The tail is approximately 450,000 years old.

Turbulence causes density variations similar to observations.

Mira likely recently entered the Local Bubble.

Abstract

Recent observations of the Mira AB binary system have revealed a surrounding arc-like structure and a stream of material stretching 2 degrees away in opposition to the arc. The alignment of the proper motion vector and the arc-like structure shows the structures to be a bow shock and accompanying tail. We have successfully hydrodynamically modelled the bow shock and tail as the interaction between the asymptotic giant branch (AGB) wind launched from Mira A and the surrounding interstellar medium. Our simulations show that the wake behind the bow shock is turbulent: this forms periodic density variations in the tail similar to those observed. We investigate the possiblity of mass-loss variations, but find that these have limited effect on the tail structure. The tail is estimated to be approximately 450,000 years old, and is moving with a velocity close to that of Mira itself. We suggest that the duration of the high mass-loss phase on the AGB may have been underestimated. Finally, both the tail curvature and the rebrightening at large distance can be qualitatively understood if Mira recently entered the Local Bubble. This is estimated to have occured 17 pc downstream from its current location.