Discovery of an HI Counterpart to the Extended Tail of Mira

TL;DR

This paper reports the detection of an atomic hydrogen tail associated with Mira, revealing its extended structure, interaction with the interstellar medium, and suggesting such tails are common in mass-losing red giants.

Contribution

First detection of an HI counterpart to Mira's tail, providing insights into its structure, age, and interaction with the interstellar medium.

Findings

HI tail extends 88' from Mira

Tail age estimated at ~120,000 years

Complex substructure observed in the HI emission

Abstract

We report the detection of an HI counterpart to the extended, far-ultraviolet-emitting tail associated with the asymptotic giant branch star Mira (o Ceti). Using the Nancay Radio Telescope (NRT), we have detected emission as far as 88' north of the star, confirming that the tail contains a significant atomic component (M_HI ~ 4x10e-3 M_sun). The NRT spectra reveal a deceleration of the tail gas caused by interaction with the local interstellar medium. We estimate an age for the tail of ~1.2x10e5 years, suggesting that the mass-loss history of Mira has been more prolonged than previous observational estimates. Using the Very Large Array (VLA) we have also imaged the HI tail out to ~12' (0.4 pc) from the star. The detected emission shows a ``head-tail'' morphology, but with complex substructure. Regions with detected HI emission correlate with far-ultraviolet-luminous regions on large scales, but the two tracers are not closely correlated on smaller scales (<1'). We propose that detectable tails of HI are likely to be a common feature of red giants undergoing mass-loss.