NGC 3521
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May 22, 2023
This pretty galaxy is NGC 3521. It is located more than 26 million light years away in the constellation Leo. The prominent dark lanes, fluffy (flocculent) texture and large halo remind me a lot of Messier 63. Although it’s classified as a barred-spiral galaxy, the bar is difficult to discern in photos. This galaxy is moderately large in the sky, covering more than 1/3 the width of the full Moon.
As usual, many other galaxies share this field with the main subject of the image. Several are highlighted in this annotated image.
Tekkies:
Acquisition, focusing, and control of Paramount MX mount with N.I.N.A., TheSkyX and PHD2. Focus with Optec DirectSync motor and controller. Equipment control with PrimaLuce Labs Eagle 4 Pro computer. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Average transparency and seeing. Data acquired April 10 – May 16, 2023 in a moonless sky.
Luminance: Sky-Watcher Esprit 150 f/7 refractor and QHY600M camera with Optolong UV/IR filter
Chrominance: Takahashi FSQ-106 ED IV @ f/5 and QHY367C Pro one-shot colour camera with Optolong UV/IR filter
61x5m chrominance = 5hr05m
Total: 10hr15m
Preprocessing: The WeightedBatchPreProcessing script was used to perform calibration, cosmetic correction, weighting, registration, local normalization and integration of all frames.
Alignment of Master Frames: DrizzleIntegration was applied to the OSC frames (within WeightedBatchPreProcessing), and the result was aligned to the Luminance master with StarAlignment. This yielded aligned Lum and Colour masters.
Gradient Removal: DynamicBackgroundExtraction was applied to both masters.
Colour Calibration: SpectrophotometricColorCalibration was used to calibrate the OSC master.
Deconvolution: BlurXterminator was used on each master with a custom psf FWHM determined with the PSFImage script, and star sharpening set to 0.10 with “Correct First” selected.
Linear Noise Reduction: NoiseXterminator was applied to each image with settings Amount=0.9 and Detail=0.15
Stretching: HistogramTransformation was applied to each image to make a pleasing yet bright image.
Nonlinear Processing
Luminance addition: LRGBCombination was applied to replace the lightness of the RGB image with the Luminance master.
Star Removal: StarXterminator was used to remove the stars, with Unscreen selected
Nonlinear Noise Reduction: NoiseXterminator was used to reduce noise in the background areas of the image with settings Amount=0.9 and Detail=0.2
Contrast Enhancement: Using a mask to select the galaxy, LocalHistogramEqualization was applied three times. A Contrast Limit of 1.5 and 1 iteration was used for each LHE application (scale 20, strength 0.35; scale 80, strength 0.18; scale 150, strength 0.18).
Sharpening: The same mask was used with MultiscaleMedianTransform to sharpen Layers 1 – 4 with strengths of 0.01, 0.03, 0.03, and 0.02, respectively.
Star Restoration: PixelMath expression combine(starless, stars, op_screen()) was used to combine the starless and stars-only images created with StarXterminator.
Final Steps: Background, galaxy and star brightness, contrast and saturation were adjusted in several iterations using CurvesTransformation and ColorSaturation, with masks as required. ICCProfileTransformation (sRGB IEC61966-2.1; Relative Colorimetric with black point compensation) was applied prior to saving as a jpg. Image was annotated with the AnnotateImage script. Finder chart was made using the FindingChart process.
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