A pair of stellar clusters in Carina

Nights when I’ve been able to get the rig out and imaging have been few and far between recently. Sometimes I have other things on that prevent me from getting out under the stars, but mostly it’s been the weather.

Of course, there have been nights when I’ve checked the cloud forecast and stayed inside, only for there to be pristine skies above me. I’m now getting to the point of (mostly) ignoring the forecasts and using my pair of Mk I eyeballs and seeing for myself what the conditions are like.

Which is exactly what I did for these two images.

As I’ve said before, stellar clusters are not my favourite target, although after seeing how NGC3532 (down below) came out (and my previous image of NGC2516) I could be tempted to image these targets more often. Many images of open clusters like this tend to over-play the blue colour of the stars to some degree, and I’m no different in that. Although I do try to keep things on the ‘reasonable’ side of artistic interpretation.

I have to say that I am extremely happy with how my rig performed. Every module of KStars/Ekos performed exactly as it should. Although the renaming of the ASI equipment to ZWO did catch me out and I needed to tweak some settings.

The auto-focus module worked perfectly, getting me pin-point stars in it’s first attempt. (Usually it heads off into the weeds and I end up running the auto-focus routine a couple of times.) But my greatest happiness was reserved for the guiding. I usually aim for 1 arc-second (RMS) of guiding error. Aside from the time a band of high cloud passed through, the guiding was running between 0.5 and 0.6 arc-seconds (RMS) error. At one stage it dipped to as low as 0.37 arc-seconds. Let’s just say that I am NOT making any changes to anything for as long as I can.

Several bands of high cloud passed through whilst I was imaging NGC2808, so I ended up sifting out a number of bad frames. By a cool coincidence, the imaging time came out to be 42 minutes, and a ’thumbs-up’ to you if you know the significance of 42.

Processing wise, it was my usual “throw everything into Siril and see what comes out the other end” workflow. Starnet++ took care of all the layer separation work, although this time around I decided to try Siril’s star recombination workflow and it seems to have worked out pretty well.

Just for fun, I decided to try Affinity Photo’s astro-stacking routine once more. I’ve never managed to have much luck with this, getting poor quality output from it. Whether this is due to poor data, I don’t really know. Feeding the same data into Siril usually gives good results.

This time, the Affinity Photo stacked data looks better than the Siril data - if you look closely, you can see that the halo around the brighter stars is significantly smaller. Also, the colour had much less of a blue tinge in the brighter stars.

I’ll keep the Affinity Photo stacking as a fall-back, and to use as a comparison to Siril if necessary.

NGC 2808

Wikipedia says:

NGC 2808 is a globular cluster in the constellation Carina. The cluster belongs to the Milky Way, and is one of our home galaxy’s most massive clusters, containing more than a million stars. It is estimated to be 12.5-billion years old.

The cluster is being disrupted by the galactic tide, trailing a long tidal tail.

Data set for NGC2808:

• Gain: 100
• Offset: 10
• Temperature: 0 degrees C
• Exposure: 20 seconds
• Frames: 126 Lights, 50 Darks, 50 each of Flats and DarkFlats (42 minutes integration in total)
• Filter: UV/IR Cut

Processed with SiriL (stacking, pre-processing, basic stretching) before tweaking in Affinity Photo v2

Equipment: SW72ED@420mm / HEQ5-Pro / ASI183MC-Pro / SV165+SV305 / Kstars/Ekos

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NGC 3532

Wikipedia says:

NGC 3532 (Caldwell 91), also commonly known as the Pincushion Cluster, Football Cluster, the Black Arrow Cluster, or the Wishing Well Cluster, is an open cluster some 405 parsecs from Earth in the constellation Carina. Its population of approximately 150 stars of 7th magnitude or fainter includes seven red giants and seven white dwarfs. On 20 May 1990 it became the first target ever observed by the Hubble Space Telescope. A line from Beta Crucis through Delta Crucis passes somewhat to the north of NGC 3532. The cluster lies between the constellation Crux and the larger but fainter “False Cross” asterism. The 4th-magnitude Cepheid variable star x Carinae (V382 Car) appears near the southeast fringes, but it lies between the Sun and the cluster and is not a member of the cluster.

The cluster was first catalogued by Nicolas Louis de Lacaille in 1752. It was admired by John Herschel, who thought it one of the finest star clusters in the sky, with many double stars (binary stars).

Data set for NGC3532:

• Gain: 100
• Offset: 10
• Temperature: 0 degrees C
• Exposure: 30 seconds
• Frames: 120 Lights, 50 Darks, 50 each of Flats and DarkFlats (60 minutes integration in total)
• Filter: UV/IR Cut

Processed with SiriL (stacking, pre-processing, basic stretching) before tweaking in Affinity Photo v2. The second image was processed using only Affinity Photo.

Equipment: SW72ED@420mm / HEQ5-Pro / ASI183MC-Pro / SV165+SV305 / Kstars/Ekos

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• Astro