NGC 5907, the Splinter Galaxy
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June 15, 2018
This spring gem is the Splinter Galaxy, NGC 5907. Through a large telescope, it looks to me like a toothpick. The photo brings out much more detail, including a bright core and a prominent dark dust lane. The Splinter Galaxy is about 50 million light years away and is made up mostly of white dwarf stars — small, dense stars nearing the end of their lives. They eventually lose all their heat and ability to fuse elements, and get cold and dark, a cinder if you will.
Many other galaxies share the field with NGC 5907, some of which are highlighted in an annotated image.
Sky-Watcher Esprit 150 f/7 refractor, QHY 16200-A camera, Optolong L, R, G and B filters, Paramount MX. Acquisition with TheSkyX. Guided with a KWIQ Guider. Focused using FocusMax 4 with Starizona Microtouch focuser. Automation with CCDCommander. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. No moon, above average transparency and fair seeing. Data acquired June 1-12, 2018.
5 and 10m subs through LRGB totaling 11hr4m).
Data Reduction and Cleanup
The BatchPreProcessing script was used to perform calibration, cosmetic correction and registration of all frames. ImageIntegration was used to make the L, R, G and B masters. DynamicCrop was used to crop all the masters identically. DynamicBackgroundExtraction was applied to each master.
Creation and cleanup of SynthL: The L, R, G and B masters were combined using the ImageIntegration tool (average, additive with scaling, noise evaluation, iterative K-sigma / biweight midvariance, no pixel rejection).
Linear Noise Reduction: MultiscaleLinearTransform was used to reduce noise in the SynthL image. An internal mask was used, with layer settings for threshold and strength as follows:Layer 1: 3, 0.7 Layer 2: 2, 0.5 Layer 3: 2, 0.45 Layer 4: 1.0, 0.10.
Stretching: HistogramTransformation was applied to the SynthL to make a pleasing, bright image.
Creation and cleanup: ChannelCombination was used to make color image from the R, G and B masters. The RGB image was processed with ColorCalibration using a preview of background sky as the background reference.
Linear Noise Reduction: MultiscaleLinearTransform was used to reduce noise in the RGB image. An internal mask was used, with layer settings for threshold and strength as follows: Layer 1: 3, 0.85 Layer 2: 2, 0.75 Layer 3: 2, 0.55 Layer 4: 1.0, 0.25.
Stretching: HistogramTransformation was applied to the RGB image to make a pleasing, bright image.
Combining SynthL with RGB
The processed SynthL was applied to the RGB image using LRGBCombine.
Noise Reduction and Re-Stretch: TGVDenoise was applied in L*a*b* mode (1000 iterations with convergence on and set to 0.004) with a range mask used to protect high signal areas. HistogramTransformation was used to raise the black point (but with no clipping).
Dynamic Range Adjustment: HDRMultiscaleTransform was applied at scales of 5 and 3 pixels to compress the dynamic range in the galaxy core, using a mask to protect background and stars. To restore contrast, LocalHistogramEqualization was applied at scales of 50 and 150 (maximum contrast 1.5 and amount 0.25 for both) using the same mask.
Sharpening: MultiscaleLinearTransform was used sharpen the structures in the core of the galaxy. Bias values in layers 2 and 3 were increased to 0.1 and 0.2, respectively. A mask was used to protect background and stars.
Final Steps: Background, cluster and star brightness, contrast and saturation were adjusted in several iterations using Curves with masks as required. Slight blotchiness of the background was reduced by increasing the brightness of dark pixels with the PixelMath expression:
iif($T<0.07, $T+0.5*(median($T)-$T), $T)
Image scale is about 1.15 arcsec per pixel for this camera/telescope combination.