sh2-132 - The heart of the Lion Nebula : with WR153ab



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The Lion Nebula is a bright emission nebula in the constallation Cepheus. In a [widefield view] of this nebula it's name becomes very apparent, but in this image I have found myself lost on many occassions, mesmerized by the different kinds of activity going on. The first (and most promonent) feature of this nebula is the waterfall-like stream of doubly ionized oxygen that cuts through the right side of the image... almost as if it's a river feeding a lake of water that is the center of the nebula below. There is also a very faint ring-like structures that can be seen in green/yellow regions. One portion of this ring really stands out quite significantly to the left of the large stream of oxygen: this illumination is where the nearby Wolf Rayet star-pair (153ab) are releasing strong intersteller winds against the nearby molecular clouds (the brown structures), rendered here as a strong green and yellow color. My favorite parts of this nebula are the darkest brown molecular clouds along the bottom, and the few smaller ones that are on the top of the image. In comparison to the yellow/green ring-structure I get the impression that the dark molecular clouds are positioned closer to us, and they are blocking a small portion of the overall illumination... Perhaps if viewed from the other side of this nebula those dark structures would appear quite a bit brighter as they seem to be ionizing from many of the O-type stars through the region. This nebula really gives a fascinating view of how these kinds of stars interact with molecular clouds.



A more detailed description of the events transpiring in this nebula can be found in the paper published in 2010 by J. Vasquez, C. E. Cappa, S. Pineault, N. U. Duronea titled Ionized gas, molecules and dust in Sh2-132



When Processing an image I like to explore new ideas and techniques, and for this image I decided to try a couple of different approachs to deriving the luminance channel from the three narrowband filters. Previously I integrated all files together to create a super luminance, but this time was reading about a technique of creating a SNR Optimized Synthetic Luminance as outlined by by Juan Conejero of the PixInsight Development team. I explored and compared my usual super luminance technique versus using Ha as luminance versus using the SNR Optimized Synthetic as can be seen in this composite image and this animated gif. I'm curious what you all think of these comparisons. I hope to write up some specifics with some conclusions on this as well as how it relates to LRGB processing at a future date.



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 5nm Ha, 3nm Oiii, 5nm Sii narrowband 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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Data Acquired using N.I.N.A and Guided with PHD2
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Acquisition Details (excluding rejected frames):

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Ha: 59x10min (9 hours 50 minutes)
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Oiii: 46x10min (7 hours 40 minutes)
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Sii: 43x10min (7 hours 10 minutes)
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Total: 24 hours 40 minutes
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The resulting image is a combination of the following steps:

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Inspected all subs for bad images with Blink, discarding 11 subs from clouds
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Calibrated all subs with their corresponding master flat and master dark
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Used subframe selector to weight Ha, Oiii, Sii separately for integrating each
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(20*(1-(FWHM-FWHMMin)/(FWHMMax-FWHMMin))

+ 10*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin))

+ 30*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin)

+ 20*(Stars-StarsMin)/(StarsMax-StarsMin))

+ 30

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Selected the best sub from subframe and blink to use as a reference frame which stacking each set
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New Created a SNR Optimized Synthetic Luminance by integrating the three resulting stacks documented by Juan Conejero of the PixInsight Development team.



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Reference Formula: Lopt = rHA*(HA + dHA) + rO3*(O3 + dO3) + rS2*(S2 + dS2)
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ImageIntegration:
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[li]Combination = Average[/li]



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[li]Normalization = additive with scaling[/li]



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[li]Weights = Noise evaluation[/li]
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[li]Scale estimator = iterative k-sigma[/li]
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[li]Generate integrated image = enabled[/li]
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[li]Evaluate noise = enabled[/li]
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[li]Pixel rejection = No rejection[/li]
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[li]Clip low range = disabled[/li]
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[li]Clip high range = disabled[/li]




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Cropped the stacking edges of the integrated masters
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Linear fit the Ha and Sii images to Oiii for the initinal color balance
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Combined the Sii as Red, Ha as Green and Oiii as the Blue channel to create a color RGB image
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Luminance Processing:

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Dynamic Background Extraction



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6 large points (Radius: 75 and 50)
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Subtraction/Normalized
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Automatic Background Extractor



[li]Function degree 1 with normalization[/li]
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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 a separate unmodified 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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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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Combination of Histogram Transformation and Masked Stretch
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Morphological Transformation (4 rounds) to shrink the overall intensity stars



[li]Took me a couple of times to get a good mask for this as evident by this blooper shot failed attempts[/li]
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Unsharp Mask on the stars to sharpen
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HDR Multiscale Transformation - 7 Layers with a mask protecting the stars
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Local Histogram Equalization - Radius 256, Contrast 2, Amount 0.3
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SHO Processing:

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Dynamic Background Extraction



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6 large points (Radius: 75 and 50)
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Subtraction/Normalized
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RGB Workingspace set to 1,1,1
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Remove Magenta from SHO Stars (Invert+SCNR Green+Invert)
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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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Remove two hot pixels that were overlooked during integration
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Combination of Histogram Transformation and Masked Stretch
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Morphological Transformation (1 rounds) to shrink the overall intensity stars
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Channel Combination in CIE L*A*B mode to add the Synthetic Luminance to the SHO color image
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Additional Star Shaping with Morphological Transformation with Star Masks and Contours based star masks
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Additional sharpening and noise reduction using ATrousWaveletTransform
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Various curves to bring the Ha background to Brown, Soften the Green Overcast, and enhance contrast
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HDR Multi Scale on the Stars to minimize halos
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