thanks everyone..
Greg - the huge hydrogen cloud at the top is part of SH2-264. Below is a map of all the features in this image which will also help in locating Abell 13 (for anyone interested).
Steve - 16 bit would certainly be nice but I don't think that Astro Pixel Processor allows anything other than 32 bit when stacking, although I do normally export 16 bit TIFF for further work in Photoshop.
