The optical emission nebulae in the vicinity of WR 48 (Theta Mus); True Wolf-Rayet ejecta or unconnected supernova remnant?

TL;DR

This study investigates nebular structures near WR 48 (Theta Mus) and concludes that the previously assumed shell is actually part of overlapping nebulosities, including a potential supernova remnant and complex H II regions, with unique ionized outflows observed.

Contribution

The paper provides new spectral and morphological analysis showing the nebular shell around Theta Mus is not a WR shell but part of larger nebulosities, including a possible supernova remnant.

Findings

The nebular shell around Theta Mus is not a Wolf-Rayet shell.

Identification of a possible new optical supernova remnant.

Detection of unique collimated ionized outflows near Theta Mus.

Abstract

During searches for new optical Galactic supernova remnants (SNRs) in the high resolution, high sensitivity Anglo-Australian Observatory/United Kingdom Schmidt Telescope (AAO/UKST) HAlpha survey of the southern Galactic plane, we uncovered a variety of filamentary and more diffuse, extensive nebular structures in the vicinity of Wolf-Rayet (WR) star 48 (Theta Muscae), only some of which were previously recognised. We used the double-beam spectrograph of the Mount Stromlo and Siding Spring Observatory (MSSSO) 2.3-m to obtain low and mid resolution spectra of selected new filaments and structures in this region. Despite spectral similarities between the optical spectra of WR star shells and SNRs, a careful assessment of the new spectral and morphological evidence from our deep HAlpha imagery suggests that the putative shell of Theta Mus is not a WR shell at all, as has been commonly accepted, but is rather part of a more complex area of large-scale overlapping nebulosities in the general field of the WR star. The emission comprises a possible new optical supernova remnant and a likely series of complex H II regions. Finally, we present the intriguing detection of apparent collimated, directly opposing, ionized outflows close to Theta Mus itself which appears unique among such stars. Although possible artifacts or a temporary phenomenon monitoring of the star is recommended.