The W4 chimney/superbubble
  A conical void in the Galactic HI within the Perseus arm has been proposed to be a chimney. However, Halpha data suggest that the structure may be closed at higher latitudes and therefore is a superbubble rather than a chimney. Recent observations have extended our view of the HI and the radio continuum emission to higher latitudes, up to 8 degrees;. The new images show the HI structure to be open at the top and a small filament suggests recent breakout. The conical shape of the structure is not easily explained by superbubble models. 
Magdalen Normandeau