NGC 6357

OTA: TAO 150 (f/7.3)

Camera: FLI - ML16200 (1.13 arcseconds/pixel)

Observatory: Deep Sky West, Chile

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: ~1.5 deg

Processed by Alex Woronow (2020) using PixInsight, Skylum, Topaz, SWT

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 bright horizontal ridge in the center of the nebula, 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, very 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: https://astrob.in/7t6qnc/0/. Fukui, et.al (2017) suggest that these two clouds collided about 10^5 years ago, which set off abundant the star formation in both clouds.

Processing Notes. Because of the low average FWHM (<2”), I drizzled all data 2x. From the six different subs (broadband and narrowband) I produce the three images posted here, which are down-sampled versions of the drizzled images. They are (A/Original) an RGBHSO image, where each narrowband sub was integrated into its equivalent broadband sub(s). By the very nature of the image combination, HII appears red, and clearly dominates everything and actually hides much of the detail in the image from our perception. Image (B) is a narrowband image with a custom mapping of SHO=>RGB; H dominates R, S dominates G, and O maps entirely into B. It shows some additional detail and some of the variability in gas compositions. The final image (C) is the V-channel from the HSV color model. V is for “value,” ... akin, vaguely, to brightness. This channel was extracted from the RGBHSO image and processed to reveal maximum detail available. In Images A and B, star colors are photometrically calibrated.