NGC2516 - The Diamond Cluster
Wikipedia says:
NGC 2516 (also known as Caldwell 96) is an open star cluster in the southern sky in the constellation Carina discovered by Abbe Lacaille in 1751-1752. It is also called Southern Beehive or the Sprinter.
This bright cluster itself is easily visible with the naked eye as a hazy patch, but is resolvable into stars using binoculars. It contains two 5th magnitude red giant stars and three main visual double stars: HJ 4027, HJ 4031 and I 29. A small telescope would be required to split the double stars, which are all pairs of 8-9 magnitude and 1-10 arcseconds separation.
NGC 2516 and the recently discovered nearby star cluster Mamajek 2 in Ophiuchus have similar age and metallicity. Recently, kinematic evidence was presented by E. Jilinski and coauthors that suggests that these two stellar groups may have formed in the same star-forming complex some 135 million years ago.
The cluster is surrounded by the 500-parsec diameter halo consisting of stars ejected from cluster
Stellar clusters aren’t really my “thing” when it comes to imaging, much preferring cool targets like nebula or galaxies. However, when I saw an image of this one, I couldn’t go past it.
I set out to replicate one of the images I saw of it - a handful of bright blue-white diamonds (complete with diffraction spikes) on a black background.
Interestingly enough, I had no technical issues with this image - the auto-focus routine ran perfectly and the auto-guiding error next got above 1 arc-second (usually it was somewhere between 0.5 and 0.7 arc-seconds, with the occasional dip below 0.5.) So I can only wonder what level of technical hell and frustration awaits me in my next imaging session…
In terms of processing, I did next to nothing with this one. The images were stacked and colour calibrated and any left-over green noise was removed via Siril’s built-in routines. Then I separated the image into a starless ‘background’ and a star-mask image. When I looked, the ‘background’ had virtually nothing in it - some left over blue noise smudges from the stars in the centre of the image and the usual dusting of light pollution noise.
I decided to forget the background and concentrate my processing on the stars. Not that they needed much - a couple of tiny tweaks with one of James Ritson’s macros and it was finished. This would have to be the quickest image I’ve ever processed…
I’m happy with both the full-size image and the cropped one. The extra negative space helps give a sense of perspective to the cluster, whilst the cropped one makes it ‘up close and personal’.
Image data:
- Gain: 100
- Offset: 10
- Temperature: 0 degrees C
- Exposure: 20 seconds
- Frames: 360 Lights, 50 Darks, 50 each of Flats and DarkFlats (120 minutes integration in total)
- Filter: UV-IR Cut
Processed with SiriL (stacking, then pre-processing, basic stretching and star removal with Starnet++) before tweaking in Affinity Photo v2
Equipment: SW72ED@420mm / HEQ5-Pro / ASI183MC-Pro / SV165+SV305 / Kstars/Ekos
Image 1 - The Diamond Cluster (full image)
