NGC 4631 and 4656 (Tom Gray)

Celestial hemisphere: Northern · Constellation: Canes Venatici (CVn) · Contains: NGC 4627 · NGC 4631 · NGC 4656 · NGC 4657 · Whale Galaxy

NGC 4631 and 4656

With May just around the corner, I wanted to have a go at some galaxies using my longer focal length refractor, before astro-dark recedes. This my third attempt to capture these wonderful ‘blue’ galaxies - in LRGB with my 183 mono camera and WO Zenithstar 80mm semi APO refractor.

NGC 4631 (the whale) is a MW sized galaxy in Canes Venatici around 25 mLY away, the brighter portions contain star forming regions and there are an abundance of younger blue star clouds. NGC 4627 (the pup) is a companion galaxy. Below are the distorted NGC 4656 and small interacting dwarf galaxy 4657, annotated and visible in my image. A faint star stream extends from this region. There are a number of other small faint galaxies in the background.

Good focus was difficult due to poor seeing, and a slight misalignment in the optical train, caused elongation of the stars. My biggest problems occurred during pre-processing, with over-correction of my flats resulting in donuts all over the place. It appears the bias frames, taken as dark-flats, were a big part of the problem; it seems the optimum settings for the 183M may not be the same as 183C. I processed without biases, and the Startools heal/repair modules enabled me to tidy up the donuts and improve the star shapes. GraXpert v3 made a good job of the gradients and the latest AI denoise worked well.

All in all I'm happy with the resulting image, but a lot of work to do to optimise this setup. Much as I have enjoyed my wide field lens, it is good to see a little more detail.

Final
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Title: Crop

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Altair Astro 183 M/C Hypercams
UK Astro-Imaging
Sky-Watcher Star Adventurer

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Status	Advanced success
Started	...
Astrometry.net job	9764936
PixInsight job	DI4XN5KCC3H3DFK1Q736AGKTX5E7CKYL
PixInsight queue size	n/a
PixInsight stage	TASK_LOG

RA (center)	12h43m06s.992
RA (top/left)	12h45m45s.378
RA (top/right)	12h39m50s.919
RA (bottom/right)	12h40m30s.800
RA (bottom/left)	12h46m21s.447

Dec (center)	+32°25′45″.79
Dec (top/left)	+32°57′41″.59
Dec (top/right)	+32°46′27″.97
Dec (bottom/right)	+31°53′37″.13
Dec (bottom/left)	+32°04′46″.46

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NGC 4631 and 4656

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