M76 - The Little Dumbbell Nebula
Along the borders of the constellation Perseus, Andromeda and Cassiopia in the winter night sky one can find a small but bright two-lobed nebula amongst the darkness of space called The Little Dumbbell Nebula. This planetary nebula is the current state of an old red giant star in the last years of its life as it sheds it's outer layers of gases into the nearby region. It is speculated that it's unique shape is caused by the presence of a second star in the system forming the gases into two primary lobes.
This image was taken on the night of December 5th 2019 on a whim while I was awaiting for the
Comet C/2017 T2 (PANSTARRS) to reach a desirable altitude in the sky. The 67% illuminated moon was up in the west approximately 60 degrees away from the target. Total acquisition time: 1.85 hours.
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AstrobinEquipment:
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Orion 8in F4.9 1000mm Newtonian Reflector
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Skywatcher F4 Aplanatic Coma Corrector
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Astrodon I Series 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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Integration Details:
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Images captured using N.I.N.A
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Red: 15x2min
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Green: 15x2min
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Blue: 15x2min
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Luminance: 15x1min
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Data was taken on the night of December 5th 2019
The resulting image is a combination of the following steps:
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Inspected all 63 subs for bad images with Blink, discarding 3
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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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Integrated all Red frames together, Blue frames together, Green frames and Luminance frames together to create masters for each filter
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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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Created a synthetic luminance image by integrating all four masters together with average, normalized additive with scaling, no-rejection, no weighting and the Biweight midvariance scale estimator
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RGB Processing:
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Dynamic Background Extraction
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Background Neutralization using 4 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 targetting luminance and chrominance
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Noise Reduction using MMT with a very protective luminance mask targetting luminance and chrominance
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Repair the saturated star cores with the HSV Repaired Separation script
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Saturation curve to soften background color gradients while holding on to star/nebula/galaxy color
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Arcsinh Stretch and Masked Stretch to bring to non-linear
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Shrink stars using a contours based star mask and morphological selection
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Luminance Processing:
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Dynamic Background Extraction
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Deconvolution using dynamic psf, 50 moffet stars, and 60 iterations
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Re-added stars with a star mask, using clonestamp and a white-reference to tailor the star mask to clean decon artifacts on stars inside of the nebula
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Noise Reduction using TGV Denoise with a low contrast mask and an autostretched local support targetting luminance and chrominance
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Noise Reduction using MMT with a very protective luminance mask targetting luminance and chrominance
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Stretched to non-linear with three rounds of masked stretch->histogram stretch to bring the tail in (with no clipping of the black point)
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Shrink stars using a contours based star mask and morphological selection
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Local Histogram Equalization with radius 30
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HDR Multiscale Transform
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Adding the Luminance to the RGB image
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Channel Combination in CIE L*A*B mode to add the luminance to the color data
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Curves to lightly increase saturation and contrast
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Cleanup star cores edges caused by masked stretch by using convolution and a star mask.
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