An unusual pair of interstellar HI features and a related white dwarf star inside the HI cavity surrounding the Upper Sco-Cen OB2 Association

TL;DR

This paper reports the discovery of two unusual interstellar HI features near a white dwarf star within a large cavity possibly created by a supernova, suggesting they may be remnants of a planetary nebula.

Contribution

It presents the identification of unique HI structures and proposes a novel hypothesis that they are remnants of a planetary nebula, expanding the understanding of interstellar gas features.

Findings

HI features are located within a large interstellar cavity.

The features may be remnants of a planetary nebula about 300,000 years old.

The cavity likely resulted from an ancient supernova explosion.

Abstract

Two mysterious unresolved HI structures at velocities of +12 and -6 km/s were discovered in high resolution 21-cm survey data in the direction of a faint white dwarf star. Examination of the HI morphology in this area of sky shows that the star and HI features exists in a large cavity in interstellar HI surrounding the Upper Sco-Cen OB2 Association. The cavity may have been created by an ancient supernova. It is hypothesized that the pair of HI features and filamentary HI structure found in its immediate vicinity may be the remnants of a planetary nebula some 3 x 10^5 years old that have cooled to the point that the gas is neutral and emitting the 21-cm spectral line. This remnant has maintained the morphological characteristics of the original planetary nebula because it expanded into a volume of space relatively devoid of interstellar gas that would otherwise have absorbed any traces of the original nebula.