M10 Globular Cluster

m10Click image for full size version

February 12, 2017

M10 is one of at least 14 globular clusters located in the constellation Ophiuchus.  Other prominent ones that I have imaged recently are M12 and M14.   M19, M62 and M107 are on my list of future targets.  Compared to most globular clusters, M10 is relatively loosely packed so is well resolved in images (and through the eyepiece).  Notice the obvious difference in star colours. The blue stars are hotter and more massive; redder star are cooler.  This cluster doesn’t have an obvious edge to my eye; it just seems to fade into the background.  It is reported to have a diameter about 2/3 that of the Moon and to contain about 225,000 stars.

This version shows far more stars than the original version from 2014 due to very different processing techniques.

Tekkies:

SBIG STL-11000M camera, Baader LRGB filters, 10″ f/6.8 ASA astrograph, Paramount MX. Guided with STL-11000′s remote guide head using 80 mm f/6 refractor. Acquisition, guiding, calibration with Maxim-DL. Image registration, integration and processing in PixInsight. Shot from my SkyShed in Guelph, Ontario. Gibbous moon. Very good transparency and poor seeing throughout.

5x10m R, 5x10m G, 5x10m B, 1x15m L and 13x10m L, all unbinned frames (total=4hr55m).

RGB
Creation and cleanup:  L, R, G and B masters were cropped and processed separately with DBE. R, G and B were combined to make an RGB image which was processed with ColorCalibration.

Linear Noise Reduction:  MultiscaleLinearTransform was used to reduce noise in the background areas. A Linear mask and the following Layer settings for threshold and strength were used: Layer 1: 3.0, 0.75   Layer 2: 2.5, 0.62  Layer 3: 2.0, 0.5  Layer 4: 0.5, 0.2, Layer 5: 0.5, 0.1.

Stretching:  HistogramTransformation was applied to make a pleasing yet bright image. During stretching, it was noted that the colours were not properly balanced for the background, so this was adjusted manually using sliders for the individual colour channels, as well as the RGB/K slider.

Synthetic Luminance:
Creation and cleanup of SynthL: The cleaned up 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 background areas. A Linear mask and the following Layer settings for threshold and strength were used: Layer 1: 3.0, 0.75   Layer 2: 2.5, 0.62  Layer 3: 2.0, 0.5  Layer 4: 0.5, 0.2, Layer 5: 0.5, 0.1.

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

Nonlinear Noise Reduction: TGVDenoise was applied with a mask to protect stars. The image was re-stretched to reset the black point. 

Combining SynthL with RGB:
The luminance channel of the RGB image was applied with LRGBCombine to make a SynthLRGB image. Colour noise reduction was used at default settings

Final Processing of SynthLRGB:
Background and star brightness, contrast and saturation were adjusted in several iterations using Curves with masks as required.

Image scale is about 1.1 arc sec per pixel.

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