The object that drew me to image this region was Sh2-224, the red wedge-shaped nebula with blue edges on the top and bottom. The nebula is located some 12,000 light-years away in the constellation Auriga and is very large at 150 light-years. The presence of hydrogen (HII) and oxygen (OIII) are characteristic of a supernova event although no progenitor star has been located. If this is a Supernova Remnant (SNR), the explosion took place approximately 60,000 years ago.
Sh2-223 sits very close to Sh2-224 and was also thought to be a SNR, however, more recent studies indicate that it is a HII emission nebula energized by a nearby star - this nebula is a bit closer to us at 7,000 light-years. Sh2-225 is also a HII emission nebula and is located about 12,000 light-years away. Another claim to fame for this nebula is that it contains a protostar designated as IRAS 05235+4033. Small but distinct, Sh2-227, is another HII nebula 80 light-years across and at a distance of 14,000 light-years.
All of these nebulae are very faint and sit in a dense but colorful starfield. An open cluster, NGC 1857, is just to the left of Sh2-227 and consists of ~40 stars. I did this project with my widefield setup which is built around a 200mm camera lens and the ZWO ASI2600MC but it would definitely be worthwhile to go back with more focal length. A fast system such as a RASA would be optimal for any of these targets since they are so dim. Using the IDAS NBZ filter which singles out HII and OIII, HII was the major component and only Sh2-224 had a clearly distinct OIII component, however, there were hints that there may be a small amount of OIII in some of the other nebulae - Sh2-227 in particular.
I planned to obtain more data but the weather gods and moon put the kibosh on that. Processing this image was very difficult because these objects were so faint. I had to do a lot of tedious processing gymnastics to isolate the nebula and even before normal processing my stacked subs had a weird gradient that DBE and GradientX could not totally fix so I had to play with that first. I separated the RGB channels to make a synthetic HOO image by using red for Ha and a combination of 70% green + 30% blue for the OIII. Lastly, there was some update by the ASIAIR where my normal gain of 100 was reset to gain 50 unbeknownst to me so I had to make a new set support frames.
Dates: 11-28, 30, 12-13, 19, 20, 29
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