Hard to say Andy. There is a curved section of Ha. I did a mosaic of the area a while ago. Mine is lower res so it doesn't show up as much but there is a curved section there. Perhaps not as definite as yours though.
http://www.pbase.com/gregbradley/ima...57168/original
I occassionally see curved rings like that on my CDK from out of shot bright star reflections. I don't see them so much now I have flocked my scope. The clue is the perfect curve.
Greg.