I was initially intrigued by the two sharply defined dark nebula that are clearly visible even in short exposures of this part of the sky. I selected a framing that also captured the nebula RCW-58 thrown off by the Wolf-Rayet star WR-40 and started integrating. After the first night's exposure it became obvious that any structures associated with the dark nebulae were going to be really faint and in the end nearly 30 hours of exposure were required to start to bring out some details.
The V-shaped nebula at top left is Dobashi 5790 and the larger W-shaped nebula towards the bottom of the image is Dobashi 5805. I had to resort to Simbad to identify these rather obscure objects (
Dobashi 2010). Apart from the two intense dark regions whose core extinction levels are 5.1 and 6.1 magnitudes respectively, grey and brown dust clouds fill most of the frame. A well-defined break affords a clearer view of the background stars.
At the bottom of the image a bluish reflection nebula surrounds the 5th magnitude star HD97583. I can't find any previous reference to this nebula in Simbad, probably due to its extreme faintness. The distance to HD97583 is just 95 parsecs; together with the almost complete absence of foreground stars in front of the darkest portions of Dobashi 5790 and 5805, this suggests that the nebula complex is located relatively close to earth.
Processing this image presented some significant challenges. The 2-3rd magnitude stars in nearby cluster IC2602 led to bright haloes that badly affected the image. I developed some custom code in Matlab to fit annular profiles to these haloes and subtract them from the final image. Notwithstanding the nearly 30-hour integration, the h-alpha emission from RCW-58 was barely visible, so I included some supplementary data
taken previously with a monochrome camera and H-alpha filter.
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