NGC 6357: Old Data With New TechniquesOTA: TAO 150 (f/7.3)
Camera: FLI - ML16200 (1.13 arcseconds/pixel)
Observatory: Deep Sky West, Chile, 2020
EXPOSURES:
Red: 19 x 300 sec.
Blue: 19 x 300
Green: 18 x 300
S: 13 x 1800
H: 9 x 1800
O: 12 x 1800
Total exposure: 21.7 hours
Image Width: 1.3 deg
Processed by Alex Woronow (2023) using PixInsight, PhotoDirector 365, Topaz Studio, and several custom scripts
NGC 6357 lies in the constellation Scorpius and is one of the most active star-forming regions known in our Galaxy. The Pismis 24-star cluster, below the whitish horizontal ridge in the nebula's center, has hollowed out the nebula by growing a bubble. The agents carving this bubble are strong stellar winds and intense radiation pressure from the very young, massive O- and B-class stars in Pismis 24. The bubble's center, near Pismis 24, clearly appears evacuated of its ionized hydrogen gas. (HII appears red in the RGBSHO image.) However, the effects of star formation sculpted the entire upper part of the cloud into a partial bubble--a crescent pointing upward.
Not far from this HII cloud lies another very active star-burst cloud, NGC 6334, shown here. Fukui et al. (2017) suggest that these two clouds collided about 10^5 years ago, which set off abundant star formation in both clouds.
Processing Notes. This is a reprocessing of the data used in
https://astrob.in/7bsm0r/0/, with some notable changes and, in my opinion, considerable improvements. The differences include the bypassing of drizzling the data and the addition of normalization of the data, the application of a substantially improved script to combine narrowband and broadband data (this time executed on starless images) to make a "true color" image, employed PhotoDirector 365 for the postprocessing, and utilized a recently developed method of projecting the completed color image onto a detailed grayscale image (in this case, the isolated emissions from Ha), which significantly improved the faint detail and controlled excessive color vibrance. I suppose I should reprocess everything I did over a year ago!
The three Images: The first image, A, was created by introducing the Ha (processed) image into Image C as a Lightness component in the L*a*b* color space. This allowed both detail and color intensity to combine. Image B utilized a projective combination of image C onto the processed Ha image. All three images used all the subframes listed at the top of this description. Image C has intense colors; the projective combination B Image has fine detail and a de-emphasized color range—overall, I find it pleasing. Image B retains the bold colors and the detail. It may be a bit much for many people, but it is not so unlikable for me. I guess either A or B, or some combination, will be what I print.
An elaboration on the last paragraph: I understand that the assignment of relative amounts of lightness into the R, G, and B channels depends on the "RGBWorkingSpace" settings. I used uniform coefficients in this rendering.
Alex Woronow 
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