Turbulent Entrainment in Mira's Cometary Tail

Abstract

Mira is a red giant star which passes through the Galactic ISM, leavingbehind a cometary tail extending over similar to 2 degrees (seen in thespectacular UV image of Martin and coworkers). H I 21 cm emission fromthis cometary tail has now also been detected. The 21 cm emission showsa velocity that decreases monotonically with increasing distances fromMira (along the axis of the cometary tail). We present a ``turbulentwake{''} model which gives a simple, analytic prediction for thevelocity of the material in the wake as a function of distance from thestellar wind source. We fit this predicted velocity versus position lawto the velocities deduced from the 21 cm observations, and find that awake with a half-opening angle of approximate to 11.8 degrees (and astellar motion and wind velocity/mass-loss rate corresponding to thevalues determined for Mira) reproduces the observations.