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M56, Globular Cluster in Lyra

Contains: M 56, NGC 6779

Technical card

Resolution: 4815x3210

Dates: May 23, 2015

Frames: 30x240" ISO400

Integration: 2.0 hours

Darks: ~20

Flats: ~30

Bias: ~50

Avg. Moon age: 4.89 days

Avg. Moon phase: 24.73%

Astrometry.net job: 666457

RA center: 289.173 degrees

DEC center: 30.185 degrees

Pixel scale: 0.930 arcsec/pixel

Orientation: 84.820 degrees

Field radius: 0.747 degrees

Locations: Home base, Yorktown, VA, United States

Description

Here is an image of the small globular cluster M56 in the constellation Lyra that I captured during the last clear night we’ve had in this region - going on a month now! I’m glad to image in this area of the sky again since it is rich with so many beautiful stars. I am particularly satisfied with the star colors in this image, so I intentionally did not crop tightly around M56 to enjoy the variety of hues. There is also a fair amount of H-alpha emission in this area that is faintly evident in the background. Maybe one day I’ll add some H-alpha data to this image to make it pop.

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Processing Workflow (PixInsight)
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Post-processing
1. Initial crop (Dynamic crop)
2. Reduce background gradient and neutralize background (DynamicBackgroundExtraction, subtraction)
3. Neutralize background (BackgroundNeutralization)
4. Set white balance (ColorCalibration; use entire image, disable structure detection)
5. Set luminance coefficients to 0.33333 (RGBWorkingSpace)
6. Reduce lightness noise (MultiscaleLinearTransform; 7 layers, noise reduction threshold 5, 1 and amount 0.5 ,0.5 to layers 1 and 2, respectively with inverted range mask, target: Lightness)
7. Non-linear stretch (MaskedStretch script; target median background 0.2, clipping fraction 0.01)
8. Reduce background brightness; increase contrast (CurvesTransformation to RGB/K)
9. Reduce background luminance noise (ACDNR to luminance with luminance mask)
10. Reduce background chrominance noise (ACDNR to chrominance with luminance mask)
11. Increase background contrast with minor S curve to background levels (CurvesTransformation to RGB/K)
12. Increase color saturation without mask to bring out the red background, typical of this region that has hydrogen gas and dust everywhere (CurvesTransformation to Saturation)
13. Reduce green (SCNR with inverted luminance mask)
14.Sharpen stars slightly (MultiScaleMedianTransform, bias +0.05 to layer 3 of 5 layers total, target Lightness)
15. Lower background brightness slightly (CurvesTransformation to RGB/K)
16. Neutralize background and set median brightness to 0.115. I found a small place just above M56 where there was minimal H-alpha emission or dust. I chose this as the background and set the median brighter than I usually would since there is certainly stuff here I am not seeing. (BackgroundNeutralization, Target Background 0.115)
17. Cosmetic correction to reduce purple cores in a few over-exposed stars. Using a smooth range mask selecting just the offending star cores, first brighten cores close to white (InterchannelCurves, Target CIE c, Reference CIE L, reduce saturation).
18. Final Crop to 8 x 12 aspect ratio (DynamicCrop)
19. Set ICC profile to sRGB for web publishing (ICCProfileTransformation)

Comments

Author

Jason Tackett
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M56, Globular Cluster in Lyra, Jason Tackett

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