2007MNRAS.381..308B

Four mosaics of deep, continuum-subtracted, CCD images have been obtained over the extensive Galactic radio continuum shell, W50, which surrounds the remarkable stellar system SS 433. Two of these mosaics in the and [O III] 5007 Å emission lines, respectively, cover a field of which contains all of W50 but at a low angular resolution of 5 arcsec. The third and fourth mosaics cover the eastern (in [O III] 5007 Å) and western (in 6548, 6584 Å) filamentary nebulosity, respectively, but at an angular resolution of 1 arcsec. These observations are supplemented by new low-dispersion spectra and long-slit, spatially resolved echelle spectra. The [O III] 5007 Å images show for the first time the distribution of this emission in both the eastern and western filaments while new emission features are also found in both of these regions. Approaching flows of faintly emitting material from the bright eastern filaments of up 100 km/s in radial velocity are detected. The present observations also suggest that the heliocentric systemic radial velocity of the whole system is 56±2 km/s. Furthermore, very deep imagery and high-resolution spectroscopy of a small part of the northern radio ridge of W50 has revealed for the first time the very faint optical nebulosity associated with this edge. It is suggested that patchy foreground dust along the ~5 kpc sightline is inhibiting the detection of all of the optical nebulosity associated with W50. The interaction of the microquasar jets of SS 433 with the W50 shell is discussed.