NGC 7635, aka the “Bubble Nebula”, is an emission nebula in Cassiopeia measuring about 8 x 15 arcminutes — it’s approximately 10,000 light years distant. The central portion of the nebula, containing the Bubble itself, was formed through the actions of a stellar wind from a massive central star.
This is mostly a narrowband rendition — contrast this image with my earlier attempt (2007).
Technical details are as follows:
RGB data was acquired in 2007 at MYHY Observatory (in the Philadelphia suburbs) using a 12.5″ OGS RC; Ha and OIII data using the RC and a Tak FCT-150, respectively, were added in 2018 — all photons were captured using the SBIG STL11K on a Paramount ME. The image includes 12 hours of Ha, 20 hours of OIII, and 4.5 hours of RGB data. Data reduction was in Maxim, image alignment and integration were in PixInsight, and all other processing was in Photoshop. It was assembled as an Ha/OIII bicolor image (modified bicolor technique wherein a green channel is synthesized from the red (Ha) and blue (OIII) channels. Finally, the RGB stars were added back using “lighten” mode.