Last night, with moral support from Rodney Ryderscope, we added the final 7 hours of 2x2 binned SII to the region immediately NW of the Swan (M17).
Original image here
We were struck by the extreme difference between what we are calling the Cygnet (centre and top of image) and the Swan (bottom right): the Swan is very strong in OIII (making it extremely bright visually), but the Cygnet is relatively much stronger in SII.
Sticking our swan-necks out, one explanation for that might be that there have been past supernova explosions in the region of the cygnet that have enriched it with SII, but it is further from the hot OB stars that would make it glow brightly in OIII. Even if that is hopelessly wrong, the difference is very striking.
Green: H-alpha 7 hrs in 1hr unbinned subs; red and blue: SII and OIII 7 hrs each in 1hr 2x2 binned subs. Total exposure 21 hrs. 3nM filters. 20 inch scope. Field approx 0.5 deg. Original image 0.55 sec arc/pixel. North is on the left.
Galaxy time now!
Best,
Mike and Trish