I noticed this interesting planetary nebula unexpectedly while inspecting images of the Bubble Nebula collected in my Bortle 4 backyard few months ago. After quick Google/AstroBin search I found just few images of it available online and one of them (probably the best) by AstroBin user Sven Eklund who dubbed it “the Croissant Nebula” and the name fits this PN perfectly.

Below is a crop of unprocessed Ha image (32 hours) with automatic stretch applied where you can see the Croissant Nebula location relative to the Bubble Nebula.



From Wikipedia, the free encyclopedia:

KjPn 8 is a bipolar planetary nebula which was discovered by M.A. Kazaryan and Eh. S. Parsamyan in 1971 and independently by Luboš Kohoutek in 1972.

Very little was published about this nebula until 1995, when it was realized that KjPn 8 sits in the center of a very large filamentary nebula, 14 by 4 arc minutes in size. This is the largest known bipolar structure associated with a planetary nebula. Narrow band images centered at Hα and forbidden line transitions of nitrogen, sulphur, and oxygen reveal pairs of bow shocks at differing position angles, indicating the presence of episodic ejection of material along a precessing jet.  The physical size of this extended nebula is approximately 4.1 by 1.2 parsecs, much larger than a typical planetary nebula, while the core nebula known prior to 1995 is only about 0.2 parsecs in diameter.

Hubble Space Telescope observations suggest that KjPn 8 might be a very rare object, formed by a binary system in which both stars had similar masses, which reached the end of the Asymptotic Giant Branch phase within 10 to 20 thousand years of each other, and entered the planetary nebula formation stage nearly simultaneously.

Two mosaic images of KjPn 8 made with the Aristarchos 2.3 m Telescope. The upper image shows Hα emission, and the lower image shows [NII] (ionized Nitrogen) emission.



The Croissant Nebula is extremely faint and difficult to process DSO target. I had 32 hours for each of S/H/O bands and 6 hours of RGB data for the stars. OIII data was very weak and showed just a few faint spots with almost no details, so I decided not to include OIII data at all.

Instead of the classical SHO palette I processed the first revision “A” as SHH image replacing OIII data with Ha but the result was not very impressive. Then, I noticed that SII signal seems stronger and fine details of nebula structures are more defined and processed the final revision “B” in HSS palette with RGB stars.

I hope you enjoy seeing the Croissant Nebula up close and personal, the largest (in angular size) bipolar planetary nebula.