3 Morphology from the HST image

Previous images of the nebula around S 119 taken with the NTT show an axisymmetric shell, with a conspicuously brighter lobe at the north east (Nota et al. 1994). The HST F656N images resolve the nebula around S 119 and show that it is approximately spherically symmetric, with an average diameter of 7 $.\!\!^{\prime\prime}$5. Assuming that S 119 is at the same distance as the LMC ($\sim$50 kpc), this corresponds to a size of 1.8 pc. With the help of the HST especially the small scale structures in and around the nebula of S 119 are clearly detected, which were not seen in previous ground-based images. A large number of these filamemtary structures can be seen in addition to the spherical main body of nebula. The most prominent ones are four filaments extending out of the nebula, two next to each other to the north-west (marked NW-1 and NW-2 in Fig. 1), one to the south (S-1), and one to the south-east (SE-1). These filaments extend beyond the nebula's main body by 0 $.\!\!^{\prime\prime}$96, 1 $.\!\!^{\prime\prime}$81, 0 $.\!\!^{\prime\prime}$96, and 0 $.\!\!^{\prime\prime}$68, respectively. On the west side, between filaments NW-2 and S-1, at the rim of the main body, numerous filaments of comparatively low surface brightness extend beyond it. Here, no clear border of the spherical main body is visible. In this region, some of the filaments appear to be even detached from the main body of the nebula.

In the east, the surface brightness of the nebula is highest, with an H$_\alpha$ surface brightness of $8\times 10^{-14}$ erg cm^-2 s $^{-1}~\sq^-\hbox{$^{\prime\prime}$ }$. This brighter area marks the region seen in seeing-limited NTT images. In the inner part of the nebula the surface brightness is quite low ($\sim$ $4\times 10^{-14}$ erg cm^-2 s $^{-1}~\sq^-\hbox{$^{\prime\prime}$ }$ on average, with some of the filaments being weaker by almost another order of magnitude). There it is far from a homogeneous structure. On the other hand, there are also knots and filaments distributed all over the nebula which are as bright as the eastern part of the nebula. This combination of unevenly high and low surface brightness features give rise to the nebula's patchy appearance.