Omega Centauri, Placidus vs ESO VST

[Placidus]

This one was fun. Forgive us if we're tickled pink. The European Southern Observatory published a very fine shot (https://www.eso.org/public/australia/images/eso1119b/) of Omega Centauri, which they speculate to be "possibly the very best portrait of Omega Centauri ever made."

Due to excellent seeing last night, we think we've come close. Don't bother looking at the thumbnail, it's at a JPEG compression of 2 out of 12, to fit the IIS size limit. Please have a look at the original.
Our shot is here. (http://www.mikeberthonjones.smugmug.com/Category/Clusters/i-zD2K8dJ/0/O/Omega%20Centauri%20RGB%2024%20min%2 0each.jpg)

Our goals were to match the ESO shot for sharpness (star size) and depth (number of extremely faint outer members), to quantitatively match the ESO shot for colour balance and saturation, and to preserve the balance between the brightness of the core and the outskirts.

The ESO shot is a slightly wider field than ours, so we've missed out on a beautiful blue star just out of field at the bottom.

Of some interest is that at a glance, the image appears close to a uniform white, but if you zoom in to actual pixels, you can see that the individual stars are quite colourful, and there are lots of "blue stragglers" about. Star by star, our star colours seem a fair match to the corresponding ESO stars.

RGB each channel 8 x 3 min subs (72 mins total). Aspen CG16M on 20" PlaneWave CDK on MI-750 fork. Field 36' arc, 0.55 sec arc/pixel. As usual, all control hardware and software, and all processing software built/written by us.

[Shiraz]

what a beautiful image - top of the class folks :thumbsup:

[topheart]

OMG !! move over ESO !

What a wonderful image.

I see you have a fantastic setup.

Congratulations!
Tim

[Placidus]

Thanks muchly, Ray and Tim.

Actually we're cheating a bit. We're comparing our shot with their 13 megabyte publication JPEG, not their HALF GIGABYTE original, which, should we ever have any way of actually looking at it, is probably hugely better (They used a 2.2 metre scope at an altitude of about 2.5 Km).

[topheart]

They were cheating then weren't they!!
Tim

[Peter Ward]

I particularly like very faint red stars in your data.

Beautifully done. :thumbsup::thumbsup:

[Paul Haese]

Cool colours and great resolution Mike and Trish. Processing looks very good.

Just one thing you might not be seeing is that stars away from the glob at the top and bottom of the image appear to have faint tails pointing downward. Can you see that? They appear to be in line with the diffraction spikes but very thick directly underneath.

All in all a fab image. :thumbsup: One of your best in my opinion.

[Atmos]

As a quick glance, they look almost identical! You both have done a fantastic job with that shot, well done! Champagne all round :rofl:

[gregbradley]

That's a ripper M and T. Its an amazing scene really, all those stars. Its a bit overwhelming.

Greg.

[multiweb]

:eyepop: Whoah! Now you need a poolroom. No excuses. :bowdown:

[Placidus]

Thanks, Tim. We don't think we could do much better without going to altitude.



Thrilled you like it. Just had a check round a representative area, comparing the faint red fellows with the ESO shot. The vast majority seem to be real, though there's the odd hot pixel.



We're delighted that you like it Paul. Those little vertical drips are a great puzzle. They've been there ever since we bought the Aspen. Weren't there before with the STL-11000M. It's not classical blooming, because they occur on faint stars as much as on bright ones. We really ought to try taking the camera off and bolting it back on at 90 degrees, to see if its optics or chip, but mechanically that would be a nightmare.




Cheers!



Thanks, Greg. The 20" isn't especially sharp, but it's good at catching photons.



Cheers, Marc! We'd done a brief 3 minute-per-channel shot last year, to test focusing. That told us we weren't going to burn out. Last night we had a couple hours to spare before the Eagle was out of the mirk, but Omega was just about straight up, and seeing was good, so it was the perfect opportunity.

[Rex]

Stunning image Mike and Trish. When you zoom in as you have said, you can see all the individual star colours which range significantly from deep red, through orange and yellow right up to the different hues of blue. Spectacular data and processing.

[strongmanmike]

Wow :eyepop: yeah, t'is a beauty guys :thumbsup:

I see the flares below the stars too, what is that?

Great stuff, maybe I will have a go tonight too :question: haven't imaged Omega for ooooh?.. over two years now :D :P

Mike

[alocky]

A magnificent image - and I think you've done a better job of compressing the range of signal into the core as well, it doesn't look anywhere near as blown out in the middle. While peeking at pixels, I couldn't help noticing a face on spiral in the lower left of the image visible through the outer part of the globular. That's astonishing.
Cheers,
Andrew.

[Placidus]

Hi, Rex! Thanks for having a peep. Glad you like it.



Thanks Mike. The flares below the stars (actually to the right of the stars as photographed - we've rotated 90 deg) remain a deep and very annoying mystery. They show up when we do an extreme stretch on an image. They're not classical blooming, because faint stars get 'em as much as bright ones.

They are always to the right (as photographed). Right-left is north-south, so they're not due to say a sticky RA gear train.

Didn't used to get them with the STL-11000M, so they seem to be something specific to the Aspen CG16M.

They appear no matter where in the sky, and no matter whether the exposure is very short or very long.

As I mentioned in reply to Paul, we really ought to unbolt the camera and rotate it 90 degrees, and see if the smears rotate with the camera (implying something funny about the chip) or whether they remain north-south, which would suggest something about optics or guiding. But the camera, off-axis guider, and filter wheel weigh a ton, are 2.5 metres up in the air, the cable runs are really tight, whinge whinge, and it's a long, nasty, anxiety-provoking job.

[cometcatcher]

Wow, one can get lost wandering around in that image.

Is that a satellite trail top right in the red channel?

[Placidus]

Cheers, Kevin. Yes it's a satellite. We probably should use data rejection to remove it. A world without satellites: No GPS, no rural internet, unreliable international calls, lousy weather prediction, and no streaks on photos!

[stevous67]

I'm not one for globular clusters, however, you have done an outstanding effort, congratulations.

Steve

[Placidus]

Thanks, Steve. We totally agree with the sentiment. If you've seen one globular cluster, you've seen many. I have a few favourites. M4 has that sheep's face line or streak across it. The Crackerjack has a kind of spray of wheat, best seen visually. 47 Tucanae is dramatically different with its yellow-moon centre. Hunting for blue stragglers is interesting because of its significance. Some are in interesting or pretty fields. There's probably no point in photographing all 150 of them.

This fellow is perhaps special to me (Mike) because it's huge, slightly elliptical, and perhaps really a galactic nucleus, but also because it was the very first thing I saw in a telescope when I was a nipper.

[RickS]

That's a great rendition of Omega, M&T!

[Placidus]

Thanks, Rick! Glad you like it.