omega centauri Omega Centauri ( NGC 5139 ) - reprocessed with new workflow

[MikeODay]

A deep look at Omega Centauri ( NGC 5139 ) 

edit: re-processed from the original exposures - April 2018

........

previous version:

Omega Centauri ( please click / tap on image to see larger and much sharper )

 

This image is an attempt to look deeply into the mighty Omega Centauri star cluster and, by using HDR techniques, record as many of its faint members as possible whilst capturing and bringing out the subtle colours of the stars, including in the core.

( re-processed from May 2017 subs - master dark added to workflow, new HDR / colour process workflow and stretched using ArcSinh )

 

Image details:

Field of view ..... 58' 32.3" x 38' 55.6"
Image center ...... RA: 13 26 50.290 Dec: -47 28 39.80
Orientation: East is up, North is to the right

Telescope: Orion Optics CT12 Newtonian ( mirror 300mm, fl 1200mm, f4 ).
Corrector: ASA 2" Coma Corrector Quattro 1.175x.
Effective Focal Length / Aperture : 1470mm f4.7

Mount: Skywatcher AZ Eq6 GT
Guiding: TSOAG9 Off-Axis-Guider, Starlight Xpress Lodestar X2, PHD2 

Camera:  
Nikon D5300 (unmodified) (sensor 23.5 x 15.6mm, 6016x4016 3.9um pixels)

Location:
Blue Mountains, Australia 
Moderate light pollution ( pale green zone on darksitefinder.com map )

Capture ( May 2017 ):
9 sets of sub-images with exposure duration for each set doubling ( 1s to 240s ) all at ISO800.

Processing:
Calibration: master bias, master flat and master dark
Integration in 9 sets
HDR combination 
ArcSinh stretch
Pixinsight March 2018

Links:
500px.com/MikeODay
photo.net/photos/MikeODay
www.flickr.com/photos/mike-oday

[Demonperformer]

Hi, Mike

Others may have more success, but on my system the picture is not displayed (just a filename) and clicking on it takes me to a 'no-picture' icon ...

[MikeODay]

1 minute ago, Demonperformer said:

Hi, Mike

Others may have more success, but on my system the picture is not displayed (just a filename) and clicking on it takes me to a 'no-picture' icon ...

Thanks for that.  I think it might be working now

 

[Demonperformer]

Yes indeed.

Just been inspired to google and it says this cluster contains 10 million stars. You seem to have captured quite a few of them. Of course, we never get to see this one from the UK, so thanks for posting.

 

[Mark at Beaufort]

Fabulous astro photo Mike. I have an ambition to see this GC which hopefully I might succeed when I visit California this May.

[MikeODay]

1 hour ago, Mark at Beaufort said:

Fabulous astro photo Mike. I have an ambition to see this GC which hopefully I might succeed when I visit California this May.

Thanks Mark, much appreciated.  I hope you have good weather for your trip.

[stevewanstall]

This is an awe-inspiring object and beautifully rendered. I hope to be able to see it one day myself on a trip further south.  I looked up how close the stars in the centre of the cluster are (According to Wikipedia :

Globular clusters can contain a high density of stars; on average about 0.4 stars per cubic parsec, increasing to 100 or 1000 stars per cubic parsec in the core of the cluster. The typical distance between stars in a globular cluster is about 1 light year, but at its core, the separation is comparable to the size of the Solar System (100 to 1000 times closer than stars near the Solar System).

However, they are not thought to be favorable locations for the survival of planetary systems. Planetary orbits are dynamically unstable within the cores of dense clusters because of the perturbations of passing stars. A planet orbiting at 1 astronomical unit around a star that is within the core of a dense cluster such as 47 Tucanae would only survive on the order of 108 years.

So, unlikely that any intelligent life will have evolved on any planets around stars in the middle of a globular cluster, but what a holiday destination for sky watching!

[MikeODay]

Sorry Steven for some reason I missed your reply and I have only just come across it as I am about to upload a new version.

Thank you for your kind words and interesting information.

Cheers

Mike

[MikeODay]

Re-processed version using my current workflow with, I think, better colour balance and better retention of subtle colours in the fainter stars.

Omega Centauri ( NGC 5139 ) in the Centaurus constellation  ( please click / tap in image to see larger and sharper )

A full size image ( ~ 6000 x 4000 ) can be found here.

[Shibby]

Smashing! You've certainly captured a lot of stars and with great colour, too. I'm jealous of your hemisphere!

[Xiga]

I never tire of looking at this Mike!

Quick question, from one D5300 owner to another. I don't use Darks myself, but I see you've just introduced them into your new workflow.

What difference exactly did you find it made? And how did you go about trying to match the temperatures? I also presume you used PI to scale it?

I'm wondering if this is more of an issue for those in warmer climates. Hmm...

[MikeODay]

4 hours ago, Shibby said:

Smashing! You've certainly captured a lot of stars and with great colour, too. I'm jealous of your hemisphere!

Thanks Lewis.  

[MikeODay]

11 hours ago, Xiga said:

I never tire of looking at this Mike!

Quick question, from one D5300 owner to another. I don't use Darks myself, but I see you've just introduced them into your new workflow.

What difference exactly did you find it made? And how did you go about trying to match the temperatures? I also presume you used PI to scale it?

I'm wondering if this is more of an issue for those in warmer climates. Hmm...

Thanks Ciaran

I purchased a D7500 as I had read that it had less read noise, was around 5 or 6 years newer technology and so I thought it would be a big improvement over the D5300.  It turned out that the D7500, whilst it had less read noise, had a lot more warm / hot pixels; so much so that even with dithering the background looked much worse than I was achieving with the D5300.  Darks helped but not enough and I sold the D7500 and went back to the D5300.  Now, in the process of testing and comparing I discovered that, whilst the D5300 has very little noise, it is still high enough that the background can still be improved with darks ( at least at the temperatures I was testing at ~ 20deg C ).

I captured hundreds of images at 250 ISO, 240 seconds and around 20deg ambient to produce a single master dark.  I have used this now for all subs where the auto scale function in the calibration tool works.  That is, I have found that PI does a good job of scaling the master dark for most exposure durations and temperatures, only failing when the duration gets too low ( say 4 to 8 seconds at ISO 250 ).  So far the temperature has been pretty warm since I started using the master dark ( > 12 deg C ) so I don't know if it will still be worth using at low temperatures.

Oh, and by the way, when I started using the master dark I also started using a pedestal as I found it was clipping the dark values.

Cheers

Mike

[MikeODay]

From SkySafari, Omega Centauri is somewhat above the plane of the Milky Way; I suppose this would mean that most of the faint surrounding stars are either outliers of the cluster or they are foreground Milky Way stars.  

Position of Omega Centauri ( NGC 5139 ) relative to the Milky Way ( credit: SkySafari - https://skysafariastronomy.com/ )

[Xiga]

35 minutes ago, MikeODay said:

Thanks Ciaran

I purchased a D7500 as I had read that it had less read noise, was around 5 or 6 years newer technology and so I thought it would be a big improvement over the D5300.  It turned out that the D7500, whilst it had less read noise, had a lot more warm / hot pixels; so much so that even with dithering the background looked much worse than I was achieving with the D5300.  Darks helped but not enough and I sold the D7500 and went back to the D5300.  Now, in the process of testing and comparing I discovered that, whilst the D5300 has very little noise, it is still high enough that the background can still be improved with darks ( at least at the temperatures I was testing at ~ 20deg C ).

I captured hundreds of images at 250 ISO, 240 seconds and around 20deg ambient to produce a single master dark.  I have used this now for all subs where the auto scale function in the calibration tool works.  That is, I have found that PI does a good job of scaling the master dark for most exposure durations and temperatures, only failing when the duration gets too low ( say 4 to 8 seconds at ISO 250 ).  So far the temperature has been pretty warm since I started using the master dark ( > 12 deg C ) so I don't know if it will still be worth using at a low temperatures.

Oh, and by the way, when I started using the master dark I also started using a pedestal as I found it was clipping the dark values.

Cheers

Mike

Very interesting Mike, thanks for the info.

Perhaps something for me to toy with myself during the bright nights ahead.

[MikeODay]

This is a comparrison between the first version made from this data ( the one that was published here ) and the new version with the same data ( new version first ).

 

 

[LukeSkywatcher]

Great stuff.