M56
M 56- Click here for full resolution
M56 is a globular cluster in the constellation Lyra. It was discovered by Charles Messier in 1779. M56 is about 32,900 light-years away from Earth and measures roughly 84 light-years across, containing 230,000 solar masses. It is about 31–32 thousand lightyears from the Galactic Center and 4.8 thousand lightyears above the galactic plane. This cluster has an estimated age of 13.70 billion years and is following a retrograde orbit through the Milky Way. The properties of this cluster suggest that it may have been acquired during the merger of a dwarf galaxy, of which Omega Centauri forms the surviving nucleus. The brightest stars in M56 are of 13th magnitude, while it contains only about a dozen known variable stars.
source: wikipedia
NGC/IC:
Other Names:
Object:
Constellation:
R.A.:
Dec:
Transit date:
Transit Alt:
NGC6779
Globular Cluster
Cluster
Lyra
19h 16m 36s
+30° 11.0’
12 August
83º S
Conditions
M56 is best visible during the summer months from June through September. At the observatory it reaches then altitudes of just over 80°. Images were taken on 7 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 M56 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 almost 14h of data was collected.
Resolution
Focal length
Pixel size
Resolution
Field of View (original)
Image center
5000 × 3333 px (16.7MP)
2585 mm @ f/7.3
3.8 µm
0.30 arcsec/px
25' x 16'
RA: 19h 16m 35.757s
Dec: +30° 11’ 03.38”
Processing
All images were calibrated using Darks (50), Flats (50) and Flat-Darks (50), registered and integrated using the WeightedBatchPreProcessing (WBPP) script in PixInsight. During integration a total of 17 frames were rejected (weight <10%). This affected mostly the amount of data from the Green filter. Looking back at the imaging reports, the reason for rejection was mostly that these images were captured towards the end of the night where the target got pretty low at the horizon, with much higher HFD values than images taken with the target high in the sky.
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 a 60% 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. When non-stellar sharpening was set at 0.9, strange structures occurred. Turning non-stellar sharpening off resulted in a much less detailed image. A setting of 0.5 turned out to give the best sharpening results without creating strange artefacts.
Luminance was stretched by careful use of GHS. 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 a bit of brightness was brought in using CurvesTransformation.
Finally noise was reduced with NoiseXTerminator and background levels were set to 0.07 to align with other images. The composition was finalised by applying a pretty decent crop.
Processing workflow (click to enlarge)
This image has been published on Astrobin.
