NGC 5466

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July 28, 2021

NGC 5466 is an ancient globular cluster. It is 12.5 billion years old, give or take 900 million years. Unlike some of its very splashy cousins, NGC 5466 has a relatively unconcentrated core.  It belongs to Class 12 of the Shapley–Sawyer Concentration Class for describing the 150 or so globular clusters that are associated with the Milky Way galaxy.  Class 12 is the most sparse. It is interesting in that it contains a particular type of blue star (“horizontal branch”).  It lies about 52,000 light years from us, and about the same distance from the centre of the Milky Way.  There are many small galaxies scattered throughout the image, some of which are shown in an annotated image I prepared. They lie much, much farther away than NGC 5466, and probably have their own groups of attendant globular clusters.

NGC5466A comparison with my 2015 image, at left, shows how my equipment and processing have changed over the last six years. Exposure times and telescope focal ratio are similar, but my new camera is much more sensitive, and my processing techniques have evolved. The 2015 image was acquired with a SBIG STL-11000M camera, Baader RGB filters and a 10″ ASA astrograph at f/6.8.

Tekkies:
Acquisition, focusing, and control of Paramount MX mount (unguided) with N.I.N.A. and TheSkyX. Focus with Optec DirectSync motor and controller. Equipment control with PrimaLuceLab Eagle 4 Pro computer. All pre-processing and processing in PixInsight. Acquired from my SkyShed in Guelph. Average transparency and seeing. Data acquired June 10-16, 2021.

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

Luminance 44x5m = 3hr40m
Chrominance 70x5m = 5hr50m
Total: 9hr30m
 
Image scale 0.72 arcsec per pixel (based on Luminance)
 

Data Reduction and Initial Processing
Preprocessing: The WeightedBatchPreProcessing script was used to create a Luminance master frame from the mono camera and an RGB master frame from the one-shot colour camera. The RGB master was registered to the Luminance master using StarAlignment.

Gradient Removal: DBE was applied to both masters using Subtraction.

Colour
Colour Balancing:  Colour was balanced with ColorCalibration.

Linear Noise Reduction: MultiscaleLinearTransform was used to reduce noise in the background areas, using an internal mask to protect bright structures. Layer settings for threshold and strength: Layer 1: 5.0 0.85, 2 iterations; Layer 2: 3.5, 0.75, 2 iterations.

Stretching:  HistogramTransformation was applied to make a pleasing, bright image, with background set to an intensity of approximately 0.10.

Lightness
Linear Noise Reduction:  MultiscaleLinearTransform was used to reduce noise in the background areas, using an internal mask to protect bright stars. Layer settings for threshold and strength: Layer 1: 3.0 0.85, 1 iterations; Layer 2: 2.0, 0.75, 2 iterations.

Stretching:  HistogramTransformation was applied to make a pleasing, bright image, with background set to an intensity of approximately 0.10.

Combining Lightness and Colour Images
LRGB Combination: The lightness image was applied to the RGB image using LRGBCombination with default settings.

Additional Processing
Compression: The core was compressed in a clone of the image and blended into the original at 15%.

Nonlinear Noise Reduction:  TGVDenoise was used in L*a*b* mode to reduce noise with a mask used to target the background areas and protect the stars (max. 1,000 iterations and convergence selected for both lightness and chrominance). 

Final Steps: Background and star brightness, contrast, and colour 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 in jpg format.