NGC2403

NGC2403

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April 3, 2015, Amateur Astronomy Picture of the Day, May 30, 2015

AAPOD May 30 2015This beautiful spiral galaxy is NGC2403.  It lies in the constellation Camelopardalis, the celestial giraffe.  It contains many pink nebulae and blue star forming regions.  It reminds me of M33 in Triangulum.  NGC2403 lies about 8 million light years away and is 50,000 light years across.    This galaxy is a member of the M81 group.

Tekkies:
SBIG STL-11000M camera, Baader RGB filters, 10″ f/6.8 ASA astrograph, Paramount MX.  Guided with STL-11000’s external guider and 80 mm f/6 Stellar-Vue refractor.  Acquistion, guiding and calibration done using Maxim-DL.  Focusing with FocusMax.  Automation with CCDCommander.  Registration, integration and all processing in PixInsight.  Shot from my SkyShed in Guelph, Ontario.  Moderate moonlight for RGB, no moon for L; gibbous to full moon for Ha.

18x10m R, 20x10m G, 21x10m B, 18x10m L and 8x20m Ha unbinned frames (total=15hr30m).

RGB:
Creation and cleanup: Ha, L, R, G and B masters were cropped.  R, G and B were combined to make an RGB image which was processed with DBE and ColourCalibration.  The Ha image was also processed with DBE and the NB-RGB Combine script was applied to blend the Ha into the RGB.  A stretched version of the Ha image was used as a mask over the RGB image.  The NB-RGB was used to replace areas exposed by the mask.

Deconvolution:  A star mask was made to use as a local deringing support. A copy of the image was stretched to use as a range mask. Deconvolution was applied (75 iterations, regularized Richardson-Lucy, external PSF made using DynamicPSF tool with about 20 stars).

Stretching: HistogramTransformation was applied to make a pleasing, but bright image.

Dynamic Range Adjustment and Stretching: HDRMultiscaleTransform was applied at 6 and 4 pixel scales, protecting bright stars with a mask. TGVDenoise was applied in RGB/K mode with default settings, followed by HistogramStretch.  A range mask was made that protected stars and background, and LocalHistogramEqualization was applied to the galaxy.

Luminance:
Cleanup:  DBE was applied to neutralize the background.

Deconvolution:  A star mask was made to use as a local deringing support. A copy of the image was stretched to use as a range mask. Deconvolution was applied (75 iterations, regularized Richardson-Lucy, external PSF made using DynamicPSF tool with about 20 stars).

Stretching: HistogramTransformation was applied to make a pleasing, but bright image.

Dynamic Range Adjustment and Stretching: HDRMultiscaleTransform was applied at 6 and 4 pixel scales, protecting bright stars with a mask. TGVDenoise was applied in RGB/K mode with default settings, followed by HistogramStretch.  A range mask was made that protected stars and background, and LocalHistogramEqualization was applied to the galaxy at a scale of 110, with a strength of 60%.

Combining Luminance with HaRGB:
The luminance channel of the HaRGB was extracted, processed and then added back into the RGB image as follows:
1. Extract luminance from the HaRGB image.
2. Apply LinearFit using the SynthL channel as a reference.
3. Use ChannelCombination in Lab mode to replace the HaRGB’s luminance with the fitted luminance from step 2.
4. LRGBCombine was then used to add L to make a LHaRGB image.

Final Processing

Small-scalestructures were isolated by making a copy of the image and applying HDRLinearTransform with 4-layersand residual unchecked. Large-scale structures were isolated by subtracting the small-scale image from the LHaRGB (no rescaling).   Colour saturation, contrast and galaxy brightness were boosted on the large-scale image.  Colour saturation was boosted on the small scale image.  Then small-scale and large-scale images were added back together in PixelMath.

Star Halo Reduction:  The deconvolution mask was processed with StarMask with the contour setting to produce a mask that revealed only the outer edges of the brightest stars.  Saturation in these areas was reduced with ColourSaturation.

Final Steps:  A contrast adjustment was applied to bright the arms and core of the galaxy, and slightly darken the background.

Image scale is about 1.1 arcsec per pixel for this camera / telescope combination.