M10
M 10- Click here for full resolution
Messier 10 (NGC 6254) is a globular cluster in the equatorial constellation of Ophiuchus. The object was discovered by Charles Messier on May 29, 1764, who cataloged it as number 10 in his catalogue and described it as a "nebula without stars". In 1774, German astronomer Johann Elert Bode likewise called it a "nebulous patch without stars; very pale". Using larger instrumentation, William Herschel was able to resolve the cluster into its individual members. He described it as a "beautiful cluster of extremely compressed stars". M10 has a spatial diameter of 83 lightyears and is estimated to be 14,300 lightyears away from Earth. In terms of metallicity, the abundance of elements other than hydrogen and helium, Messier 10 is "moderately metal–poor". The abundance of iron is only 3.5% of the abundance found at the surface of the Sun. The cluster is currently located about 16,000 lightyear from the Galactic Center. It completes an orbit around the Milky Way galaxy about every 140 million years, during which it crosses the plane of the galactic disk every 53 million years.
source: wikipedia
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NGC6254
Globular Cluster
Cluster
Ophiuchus
16h 57m 09s
-04° 05.9’
08 July
48º S
Conditions
M10 is best visible during the summer months of June through August. At the observatory it reaches then altitudes in the 40-50° range. Images were taken on 9 different nights during August 2024, from IC observatory in Oria, Spain.
Equipment
The default rig at the observatory was used. The core of this rig is a Planewave CDK-14 telescope on a 10Micron GM2000 mount, coupled to a Moravian C3-61000 Pro full-frame camera. The RoboTarget module in Voyager Advanced automated the process to find optimal time-slots during astronomical night.
Telescope
Mount
Camera
Filters
Guiding
Accessoires
Software
Planewave CDK14, Optec Gemini Rotating focuser
10Micron GM2000HPS, custom pier
Moravian C3-61000 Pro, cooled to -10 ºC
Chroma 2” LRGB unmounted, Moravian filterwheel L, 7-position
Unguided
Compulab Tensor I-22, Windows 11, Dragonfly, Pegasus Ultimate Powerbox v2
Voyager Advanced, Viking, Mountwizzard4, Astroplanner, PixInsight 1.8.9-3
Imaging
One of the key objectives with star clusters is to resolve as many stars as possible, also in the center. For M10 it turned out that the regular exposure times of 180s for luminance and 300s for the RGB channels were sufficient to resolve the stars. Overall more than 14h of data was collected.
Resolution
Focal length
Pixel size
Resolution
Field of View (original)
Image center
8000 × 5313 px (42.5MP)
2585 mm @ f/7.3
3.8 µm
0.30 arcsec/px
40' x 26'
RA: 16h 57m 09.539s
Dec: -04° 06’ 05.10”
Processing
All images were calibrated using Darks (50), Flats (50) and Flat-Darks (50), registered and integrated using the WeightedBatchPreProcessing (WBPP) script in PixInsight.
Red, Green and Blue channels had their gradient removed (GraXpert), combined, calibrated (SPCC), and deconvolved (BXT). Stretching was done by multiple runs of GeneralisedHyperbolicStretch (GHS). The first one was run in Colour mode instead of RGB mode, with an 80% RGBBlend. This preserves the colours a lot better than regular RGB stretching. Stretching of the RGB image was done very mildly, to keep brightness low and colour intensity high. Colour was further smoothened using a mild convolution.
The luminance had its gradient removed as well with GraXpert. BlurXTerminator was used to sharpen the image. The image being a star cluster, the star sharpening was set quite aggressively at 0.4. The non stellar sharpening was left at 0.9, assuming this would not do much as there was no non-stellar signal. But at this setting, BXT created a lot of worm-like structures right in the middle of the cluster. Apparently the algorithm thought that some dense star patterns were actually patterns of non-stellar origin. A setting of 0.5 was low enough to not create these artefacts. The non-stellar sharpening definitely helped with the image overall, even though there was no non-stellar signal. But setting the slider at 0 had a much lower effect than a setting somewhere in the mid-range.
Luminance was stretched by careful use of GHS and HT. The image was stretched only mildly. Too bright luminance would wash-out the colours later. So the center of the cluster had typical brightness values not exceeding 0.8. This made the luminance look a bit dim. An additional little touch of sharpness was achieved with UnsharpMask.
The luminance was now blended with the RGB image, using LRGBCombination. As per the plan, the colours came through still very intense. So much so that saturation was lowered a bit using CurvesTransformation. The overall image was still a bit dim though, so in little steps some brightness, especially in the mid-range, was added using CurvesTransformation. That was also a good moment to add a little bit of contrast.
Finally noise was reduced with NoiseXTerminator and background levels were set to 0.07 to align with other images. The composition was finalised by cropping the image just a bit.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
