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

Abstract

During searches for new optical Galactic supernova remnants (SNRs) in the high-resolution, high-sensitivity Anglo-Australian Observatory/United Kingdom Schmidt Telescope Hα 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 (Θ Muscae), only some of which were previously recognized. We used the double-beam spectrograph of the Mount Stromlo and Siding Spring Observatory 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 Hα imagery suggests that the putative shell of Θ 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 SNR and a likely series of complex H ii regions. Finally, we present the intriguing detection of apparent collimated, directly opposing, ionized outflows close to Θ Mus itself which appears unique among such stars. © 2009 RAS.