M5
M5 Globular Cluster - Click here for full resolution
Messier 5 or M5 is a globular cluster in the constellation Serpens at a distance of 24,5 thousand light years. It was discovered by Gottfried Kirch in 1702 when he was observing a comet. Charles Messier noted it in 1764 and —a studier of comets— cast it as one of his nebulae. William Herschel was the first to resolve individual stars in the cluster in 1791, counting roughly 200. Messier 5 is receding from the Solar System at a speed over 50 km/s.
source: Wikipedia
NGC/IC:
Other Names:
Object:
Constellation:
R.A.:
Dec:
Transit date:
Transit Alt:
NGC5904
Rose Cluster
Star Cluster
Serpens
15h 18m 33.75s
+02º 04’ 57.7”
28 May
55º S
Conditions
M5 is best visible from early spring to mid-summer. During these April sessions, M5 was high in the sky towards the end of the night, which made it a perfect target to photograph after other targets had moved towards too low altitudes. The crescent moon was below the horizon during imaging this target in all sessions.
Equipment
The standard rig at the remote observatory, built around a Planewave CDK-14 telescope coupled to a Moravian C3-61000 Pro full-frame camera, was used to image M5. The RoboTarget module in Voyager Advanced allowed automatic scheduling to start M5 as soon as other targets had lost the required altitude of 30°.
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” RGB unmounted, Moravian filterwheel “L”, 7-position
Unguided
Compulab Tensor I-22, Windows 11, Dragonfly, Pegasus Ultimate Powerbox v2
Voyager Advanced, Viking, Mountwizzard4, Astroplanner, PixInsight 1.8.9-2
Imaging
The field of view of 0.8° x 0.5° was only just enough to capture the wide spread of the stars in this cluster. The image was captured using only RGB filters and individual frames were exposed for 180s at gain 0. Well over 10h of data was collected, but during image processing, 25 frames were rejected based on a minimum weighting factor of 0.4.
Resolution
Focal length
Pixel size
Resolution
Field of View
Image center
9526 × 6340 px (60.4 MP)
2563 mm @ f/7.2
3.8 µm
0.30 arcsec/px
47' 52.4" x 31' 51.7"
RA: 15h 18m 32.774s
Dec: +2° 04’ 54.54”
Processing
All images were calibrated using Darks (50), Flats (25), registered and integrated using the WeightedBatchPreProcessing (WBPP) script in PixInsight to R, G, B images. A very mild, mostly linear gradient was removed using the new PixInsight process GradientCorrection. The results of the GradientCorrection tool were quite good, but not a lot of gradient had to be removed to start with.
Processing was pretty standard. Platesolving using ImageSolver, which worked without any problem this time. SpectroPhotometricColorCalibration (SPCC) to get the correct colour balance. Then BlurXTerminator (BXT) using only stellar adjustments, and sharpening set at 0.35.
Stretching was a delicate business. The goal was to resolve all individual stars, even in the center. And with at globular cluster, that can be quite challenging. The approach taken here was to first do a mild stretch using GeneralisedHyperbolicStretch (GHS) in colour mode and blending at 0.7 and a very low local intensity. This allows to bring out the colours quite nicely. Then two small stretches with HistogramTransformation (HT) were applied and at this stage it was clear that the center was about to clip if not careful. So one run of HDRMultiscaleTransform was applied, which helped a lot to balance the brightness in the center with its surroundings. A final stretch with HT completed the stretching. CurvesTransformation (CT) was used to boost a bit of colour and contrast. Separately the ColourSaturation process was used to give an overall boost to the colour in the image. NoiseXTerminator (NXT) was used at a setting of about 0.7 to reduce the noise and BackgroundNeutralization was used to set the background level to 0.07, so that between images backgrounds show a similar black-value.
In the bottom of the image, there was a part of a spike of the very bright star 5 Serpentis. The field of view was too small to capture the actual star and the cluster at the same time. And without the actual star in the image, just a piece of the spike looked a bit strange. So this was cloned out using Photoshop for the final image
Processing workflow (click to enlarge)
This image has been published on Astrobin.
