SH2 200 is an old low surface brightness planetary nebula in Cassiopeia.
A feature not not well described in research literature is known as ISM-type haloes. This is a type of structure that represents ambient interstellar gas in the vicinity of a planetary nebula but is not physically related to it. Although SH2 200 is very old and highly evolved, it still has very hot and energetic central stars, which are the remnant cores of the original star that died and ejected its outer gaseous layers. The energy output of some planetary nebula central stars is so powerful that it is capable of ionizing unrelated gas in the surrounding vicinity.
Imaged in Ha HOO and RGB OTA Planewave CDK 17 at Dark Sky New Mexico.
Image Processing: Mark Hanson and Mike Selby