SH2-82 | The Little Cocoon (Kevin Morefield)

SH2-82 | The Little Cocoon

10-2023 Re-Edit: I've been looking back at some of my disappointing images to see if new software and what I've learned since can help. BlurX star reduction, NoiseX, SPCC, and some nuances I've learned with the Curves tool helped a lot here. But I think the key was using StarX to separate the stars and nebula was the biggest advance. Being able to optimize the nebula stretch without stars prevented the stars blowing up as it went after the faintest parts.

Often called the Little Cocoon or the Little Trifid, SH2-82 combines emission, reflection, and dark nebulae and is set within the star clouds of Sagitta. I think it more resembles the Cocoon Nebula than the Trifid but in any case is much dimmer than either.

I've always felt the Cocoon was really easy to process but SH2-82 was harder. There seems to be a light haze of gas softening the left half of the FOV. The nebulosity is dim enough that a fairly aggressive stretch is needed which makes the stars in the star cloud oppressively dense. More data, especially in the color channels, might be called for. I did not try shooting Ha, which is odd for a Sharpless object! Maybe that would bring more definition to the emission portion of the nebula.

PI Sub-frame selector confirmed that using the color masters and the Luminance master to create a SuperLuminance did indeed improve SNR. Since I shoot color 1x1, this did not increase my FWHM. I usually find that a SuperLuminance is an improvement over just a the Luminance data.

Color balance was done with PCC. This showed a very tight plot and the colors look right. Using the old PI color Calibration tool with structure detection on gave a decidedly green cast to things so I stuck with PCC here.

I tried many different stretches and ended up using a stretch from good old CCDStack for the color and background luminance. I then overlayed from PI a combo stretch of ArcSinh and Histogram transform for the brighter parts of the luminance. This was to take advantage of the smaller star sizes ArcSinh brings and the faint nebulosity the more aggressive stretch from CCDStack brought. They were combined using a luminance mask in Photoshop.

Original
B
Final
D

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Status	Advanced success
Started	...
Astrometry.net job	6161970
PixInsight job	8JH3QO62BCUXK9DKHW7V92K6LUBGXJN7
PixInsight queue size	n/a
PixInsight stage	TASK_LOG

RA (center)	19h30m56s.745
RA (top/left)	19h31m08s.326
RA (top/right)	19h32m39s.503
RA (bottom/right)	19h30m45s.830
RA (bottom/left)	19h29m14s.272

Dec (center)	+18°24′43″.55
Dec (top/left)	+17°57′18″.74
Dec (top/right)	+18°37′43″.90
Dec (bottom/right)	+18°52′09″.40
Dec (bottom/left)	+18°11′45″.59

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