In the center of this image lies two galaxies that are interacting. The one on top is quite a bit bigger than the one on the bottom right and in the past the one on the bottom seemed to have run through the middle of the top one forming a bridge between the two. Their interaction has left an interesting spiral pattern in the top galaxy from the tidal forces involved at this galactic scale.
I came across this target last night while wrapping up acquisition on the Heart Nebula when I stumbled upon
sky-watcher (johny)'s latest image of ARP 273 (UGC1810 - 1813) I was so transfixed by how exciting this target looked in his image I immediately pulled it up in my atlas and saw it was still in a great part of the sky to image (straight up!) so I just had to switch gears and check it out for myself. When the first frame came in I knew my plans for the night were immediately changed, and so I set up a sequence in
N.I.N.A to let it acquire data until it reaches the meridian. I did a quick stack of the while I moved to my origionally planned target (LBN777) and the initial stack looked like an almost-finished work by itself. So I decided to go ahead and follow it down the other side of the meridian to see what the rest of the night could yield, and then gave myself a challenge... If Johny could create such a great image with only 4 hours of data at f/4 maybe, given seeing conditions were fairly decent tonight (and cgem was actually behaving for once) could I come up with a half-decent result. In the end I ended up with 40 minutes of each R, G, and B filters and an hour 20 minutes of luminance and this morning sat down to see what I could do.
Thanks Johny for the inspiration!
Equipment:
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Orion 8in F4.9 1000mm Newtonian Reflector
[li]Flocked / Primary mirror replaced due to turned-down-edge[/li]
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Skywatcher F4 Aplanatic Coma Corrector
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Astrodon I Series L, R, G, B broadband filters
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ASI183mm Pro cooled to -15C
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Celestron CGEM Mount
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Self tuned / hacks to get guiding stable include:
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Intentional offset polar alignment so dec always pulses in one direction
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Balance "west" heavy (rather than the recommended east) so that the ota "falls" onto the gear teeth rather than get "lifted"
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Factor Reset hand-controller daily (to prevent cgem from being possessed and forgetting where the meridian is on subsequent night)
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Dither in RA only
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Red: 20x2min
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Green: 21x2min
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Blue: 20x2min
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Lum: 37x2min
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The resulting image is a combination of the following steps:
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Inspected all 101 subs for bad images with Blink, discarding 3 (keeping 97)
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Calibrated all subs with their corresponding master flat and master dark
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Used subframe selector to weight all subs together using the following formula:
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(30*(1-(FWHM-FWHMMin)/(FWHMMax-FWHMMin))
+ 20*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin))
+ 15*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin)
+ 20*(Stars-StarsMin)/(StarsMax-StarsMin))
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Selected the best sub from subframe and blink to use as a reference frame in stacking
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Created a super luminance by integrating all 97 frames together
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Integrated all Red frames together, Blue frames together and Green frames together to create masters for each color
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Cropped the stacking edges of the integrated masters
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Combined the Red, Green and Blue masters to create a color RGB image
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Superluminance Processing:
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Automatic Background Extractor
[li]Function degree 1 with normalization[/li]
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Independently produce a noise reduced image and a sharpened image
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Noise Reduction was done using TGV Denoise with a low contrast mask and an autostretched local support and MMT with a very protective luminance mask
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Deconvolution was done on a separate copy of the luminance with
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No deringing
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wavelet regularization with 5 layers and strong but reducing amounts/thresholds
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A starmask was created from the Noise Reduction copy to replace the stars with the origional superluminance, eliminating the ringing artifacts from deconvolution as similarly documented by /u/OkeWoke
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The noise reduced copy and the sharpened copy were combined using a luminance-based mask where the high-signal areas were filled in from the deconvolution copy and the low-signal areas were filled in from the noise reduction copy:
Decon*CombineMask+NR*~CombineMask
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Two rounds of Masked Stretch was used with no clipping and a background reference created from 5 preview windows and the Preview Aggregator script. Between each round the histogram transformation tool was used to bring the tail in without clipping and gentle noise reduction was performed in between the two stretches.
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RGB Processing:
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Automatic Background Extractor
[li]Function degree 1 with normalization[/li]
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Background Neutralization using 5 preview windows and the Preview Aggregator script as the background reference
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Color Calibration using Photometric Color Calibration using the Average Spiral Galaxy as the white reference
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Noise Reduction using TGV Denoise with a low contrast mask and an autostretched local support
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Noise Reduction using MMT with a very protective luminance mask
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Repair the saturated star cores with the HSV Repaired Separation script
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Arcsinh Stretch and Histogram Stretch
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SCNR Green on the background with a luminance mask
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Noise reduction with ACDNR to smooth out the background of the color image
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Power of Inverted Pixels and Curves with a luminance mask to brighten and adjust saturation of the high-signal areas
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Star reduction using the Morphological Selection
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The super luminance and the RGB image were then combined using the Channel Combination tool in CIE L*A*B mode.
A final gentle s-curve and saturation curve was applied at the end to produce the final image.
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