The RCW 114 nebula: An old supernova remnant or a WR wind-blown bubble?

We present medium resolution spectra (R ~ 7 km s^-1) of the interstellar NaI D1 & D2 absorption lines observed towards 7 early-type stars with distances ranging from 221 to ~ 1.5 kpc in the line-of-sight to the RCW 114 nebula. Our observed pattern of absorption is in conflict with the findings of Bedford et al. (1984) who placed an upper limit to the distance to this nebula of <200 pc. Instead, our spectral data are consistent with a marked increase in NaI absorption complexity occuring only for sight-lines with distances >1 kpc. A similar pattern of absorption behavior is seen for the SiII lambda 1304 Å interstellar line observed in the ultraviolet towards four of the aforementioned stars. We propose a scenario in which the absorption components with velocities <-10 km s^-1 seen towards RCW 114 are caused by an expanding stellar wind-blown bubble associated with the Wolf-Rayet (WR) star, HD 156385 (d ~ 1.5 kpc), and that the Hα and [SII] nebular emission probably arises in shocked filamentary gas associated with a pre-existing evolved supernova remnant cavity produced by the high-mass progenitor of the present WR star.