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March 6, 2024

M82 is a rather famous irregular galaxy in Ursa Major, the Great Bear constellation, which is easily observed through the eyepiece of my 10″ f/6 reflector. Of course visually it is just a grey smudge, not the beautiful, colourful object shown in this image.

M82 lies about 11 to 12 million light years away, and has a diameter of almost 41,000 light years. It has a high rate of forming new stars, and is known as a starburst galaxy. It’s a neighbour of M81, lying just a million light years apart, as shown in this image of the two taken several years ago. A couple ofvery distant galaxies are identified in the annotated image of this field. I’ve presented this image with south up because I thought it looked best that way (most of my images are displayed with north up).

Acquisition, focusing, and control of Paramount MX mount with N.I.N.A., TheSkyX and PHD2. Primalucelab low-profile 2″ Essato focuser and ARCO rotator. Guiding with PHD2. Equipment control with PrimaLuce Labs Eagle 4 Pro computer. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Data acquired under variable moonlight and average or worse transparency and seeing between February 19 – March 5, 2024.

Celestron 14″ EDGE HD telescope at f/11 (3,912 mm focal length) and QHY600M camera binned 2×2 with Optolong filters.

142 x 1m Red = 2hr 22m
140 x 1m Green = 2hr 20m
132 x 1m Blue = 2hr 12m
98 x 5m Ha = 8hr 10m

Total: 15hr 04m

Image scale 0.4 arcsec per pixel

Finder Chart and Annotated Image:
Data Reduction and Linear Processing

Preprocessing: The WeightedBatchPreProcessing script was used to perform calibration, cosmetic correction, weighting, registration, local normalization and integration of all frames.

RGB master: A master RGB image was made from the Red, Green and Blue masters using ChannelCombination in RGB mode.

Gradient Removal: DBE was used to remove gradients from the RGB and Ha masters. 

Colour Calibration: SpectroptometricColorCalibration was used to calibrate the RGB master. 

Deconvolution: BlurXterminator was applied to the two masters with Automatic psf , star sharpening set to 0.4, and non-stellar set to 0.9. 

Star Removal:  StarXterminator was used to remove the stars from both masters, with default settings, except Large Overlap was selected. Only the RGB stars-only image was retained.

Linear Noise Reduction: NoiseXterminator was applied to the both masters with settings Amount=0.9 and Detail=0.25

Ha Continuum Subtraction: The ContinuumSubtraction script was used to remove continuum emissions from the Ha image.

Stretching:  HistogramTransformation was applied to both masters to make pleasing images. Approximate background level after stretch was 0.08 for Ha and 0.10 for RGB.

Nonlinear Processing

Addition of Ha to RGB: PixelMath was used to blend the Ha master into the RGB image using the following expression with parameter values a=1.5 and b=0.10.

          Red:      max($T[0], a*Ha)
          Green:  $T[1]
          Blue:      iif($T[0]<a*Ha, $T[2] + b * Ha, $T[2])

Nonlinear Noise Reduction: NoiseXterminator was used to reduce noise in the background areas of both masters with Amount=0.9 and Detail=0.15.

Re-stretch: HistogramTransformation was used to boost contrast by moving the dark point to the toe of the histogram and slightly decreasing the mid-point slider.

Contrast Enhancement: LocalHistogramEqualization was applied twice. A Contrast Limit of 1.5 and 1 iteration was used for each LHE application (scale 40, strength 0.25; scale 125, strength 0.18).

Sharpening: MultiscaleMedianTransform was applied. (Layers 1 – 3 with strengths of 0.01, 0.06, and 0.07, respectively), using a mask to select only the galaxy.

Contrast, Brightness and Colour: Background and galaxy brightness, contrast, and saturation were adjusted in several iterations using CurvesTransformation with masks as required.

Stars-only steps: HistogramTransformation was applied to the RGB stars-only image. A mask was made by using ChannelExtraction to extract the luminance from the image. CurvesTransformation CIE c* slider was used to add boost colour in the stars through the star mask. A mask was made to select the largest stars and CurvesTransformation was used to make them a little smaller.

Star Restoration: PixelMath expression combine(starless, stars, op_screen())  was used to combine the starless HaRGB starless image with the stars-only image. 

Final Steps: Background, galaxy, and star brightness, contrast, hue, and saturation were adjusted in several iterations using CurvesTransformation with masks as required. ICCProfileTransformation (sRGB IEC61966-2.1; Relative Colorimetric with black point compensation) was applied prior to saving as a jpg.  The finder chart was made using the FindingChart process. The annotated version was made using the AnnotateImage script.