NGC 7635

NGC 7635, also known as the Bubble Nebula, Sharpless 162, or Caldwell 11, is an H II region emission nebula in the constellation Cassiopeia. The nebula lies close to the open cluster Messier 52. The "bubble" is created by the stellar wind from a massive hot, 8.7 magnitude young central star, SAO 20575 or BD+60°2522, which is thought to have a mass of about 44 solar masses.

The nebula is near a giant molecular cloud which contains the expansion of the bubble nebula while itself being excited by the hot central star, causing it to glow. NGC 7635 was discovered in November 1787 by William Herschel.  

The image below is largely dominated by H_alpha emission. The exposure using a narrow O[III] filter  resulted in a very faint signal, overwhelmed by H_alpha.