Mirach's Ghost - NGC404
Mirach is a bright Red Giant star that sits right between the Andromeda (M31) and the Trapezium (M33) galaxies in our night sky. A fuzzy glow appears right next to Mirach but it's light comes from much further away... far far beyond the edges of our galaxy and even beyond the local group of galaxies we live in... Yet appearing as if its next to Mirach, this fuzzy glow is an lenticular galaxy NGC404: to some known as Mirach's Ghost and is over ten million light-years away.
This image was taken across four overcast nights in late December. Only the best 72 minutes worth of data were used.
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AstrobinEquipment:
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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 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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Acquisition Details:
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Images captured using N.I.N.A
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Red: 24x1min
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Green: 24x1min
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Blue: 24x1min
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Data was taken across multiple nights between December 25th, December 26th and December 30th. As the weather has turned more cloudy and overcast I opted to discard the Luminance data, and only keep the best R, G, and B data that didn't have halo forming around the secondary brightest stars in the frames.
The resulting image is a combination of the following steps:
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Inspected all 150 subs for bad images with Blink, discarding 78 (keeping 72)
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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 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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RGB Processing:
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Dynamic Background Extraction
[li]Careful placement of DBE points with lots of trial-and-error to prevent the largest star halo from causing gradient issue.[/li]
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Background Neutralization using 3 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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Arcsinh Stretch and Histogram Stretch to bring to non-linear
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Additional curves transformation to increase overall contrast and increase color saturation
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Additional stretch with inverted luminance and Power of Inverted Pixels
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Order: 2.0
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Smoothing: 1.2
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Lightness Mask: Checked
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Additional HDR Multiscale Transformation using an inverted luminance mask to reduce the overall brightness of Mirach to better reveal NGC404
[li]7 layers and 2 iterations[/li]
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Agressive Noise Reduction on star chrominance
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Motion Blur Deconvolution on the star cores to minimize the impact of star trails from poor guiding in RA
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