Ngc 7793

[RickS]

This galaxy is described as a chaotic spiral and is a member of the Sculptor group. It was imaged over 5 nights under generally poor conditions (intermittent clouds and mostly bad seeing.) I would have liked more data and the luxury of dumping some of the weaker subs but the weather didn't allow it this year.

I do particularly like the assortment of small fuzzies in the background. There's also a pink spot on the outskirts of the galaxy at about 5 o'clock which is apparently a microquasar composed of a normal star and a stellar-sized black hole.

Scope: Ceravolo C300 @ f/9 = 2760mm FL, Atlas focuser
Mount: AP900
Camera: U16M
Filters: Astrodon E series Gen 2 LRGB
Guiding: Lodestar / MMOAG
Image scale: 0.67 arcsec/pixel
Exposures: 19x1200s L, 8x900s R, 7x900s G, 9x900s B

High res version, warts and all, can be found on Astrobin: http://www.astrobin.com/133431/

Thanks for looking. Constructive comment is appreciated :thumbsup:

Cheers,
Rick.

[RobF]

Beautiful field, lovingly processed Rick. Its such a pleasure to swim around the big field of the U16 at that res. I shudder to think it could be any better if you had encountered better conditions.

Will have to head off the books. Not familiar with this one, but congrats on the outcome.

[Amaranthus]

Excellent - a real 'Grand Design' spiral.

[E_ri_k]

I like it :thumbsup: Looks very sparkly. Heaps of faint fuzzies in the background, good job :)
Erik

[strongmanmike]

Yeah looks like the seeing has affected it slightly but still a great shot, living in average Oz and not the Chilean Andes we can't only image when the seeing cooperates, poor seeing doesn't invalidate an image, lots to like here, the colour and brightness are great :thumbsup:

Mike

[ozstronomer]

Very Nice Rick, love the small galaxy straight above the main object :thumbsup:

[DJT]

That's a lovely image Rick. Nice and sparkly as said earlier and great detail.

:thumbsup:

[Placidus]

A wonderful, deep shot, Rick. I had in ignorance thought of this galaxy as a "semi-dwarf", and therefore perhaps rather irregular, but you've shown that there's lots of beautifully photogenic regular structure, reminiscent of NGC 300 for example. You've also captured a great deal of form and colour in the little fellows in the background. Yum.

[alpal]

Nice shot Rick,
I think it would look better if you adjusted the contrast using curves
of just the bright part of the galaxy - using a blurred mask.
I'll post an example if you want?

cheers
Allan

[Shiraz]

What a beautiful image Rick - as others have said, it sparkles. A remarkable result for what was clearly fairly ordinary seeing.

[RickS]

Thanks, Rob.



Ta, Barry.



And thanks, Erik!



Thanks, Mike. It didn't turn out badly but I know the gear (and even my processing) is capable of better. That's life ;)



Thanks, Geoff.



Thanks, David.



Very kind of you, Mike.



I've tried quite a lot of different ideas on this one, Allan. If you have any suggestions feel free to give it a go.



Thanks, Ray!

[atalas]

Very nice Ric...looks like you were looking for a halo me think.

[alpal]

Rick,
Here is a go with your small pic:
Contrast with feathered blurred mask on galaxy
LAB to give more yellow at center of galaxy using feathered mask
1 pixel sharpening with mask at center feathered.
(only 5 minutes work )

Is this better?

cheers
Allan

[Bassnut]

Very tastefully done Rick, a pleasure to view. Its amazing how many background galaxies are in the pic.

[marc4darkskies]

Nice to look at and a very respectable result for 0.67"/pix in poor seeing Rick!! Very pretty field with lots to look at too. I too would try to add some more contrast into the galaxy to bring out the structure - probably using proper unsharp masking (i.e. not the PS filter) & curves.

I like that Ceravolo of yours! :)

Cheers, Marcus

[Paul Haese]

Nice work Rick. Good colour and a good field of view. Good detail despite the conditions you had.

[Rex]

This is a beautiful shot Rick. How many spiral arms has that thing got????? Imagine being on a planet in that bad boy and looking at the night sky and seeing the spiral arms above. Love the background fuzzies as well. Really nice galaxy, I have resolution envy lol.

[Stevec35]

Nice NGC 7793 Rick. Makes mine look a bit insipid.

Cheers

Steve

[RickS]

Thanks, Louie. I'm a sucker for a halo :)



Looks better at that small scale, Allan. I've done a bit of a tweak myself. See below...



Thanks, Fred!



Thanks, Paul.



It's an odd one, Rex. Thanks for the kind comments.



Thanks, Steve. I usually go a bit over the top. I thought yours was very nice but conservatively processed.

[RickS]

Thanks for the feedback, Marcus. I did a bit of wavelet hokey-pokey. Is this something like what you had in mind?

Old: http://www.astrobin.com/133431/0/
New: http://www.astrobin.com/133431/B/

Cheers,
Rick.

[RobF]

Me likes hokey-pokey'd version even more :thumbsup:

[RickS]

Thanks, Rob :D

[strongmanmike]

Hmmm? Think I like the brightness of the original actually...but line ball really :)

Mike

[alpal]

Rick,

Hi Rick,
Yes - that's much better.
You also have the red nebulas much larger than I got from the smaller pic.
I pushed the yellow core a bit more with a mask which I suppose is cheating
but it looks a bit better.
I also sharpened the masked galaxy - I think it can still take a touch more on your effort.

cheers
Allan

[cometcatcher]

Awesome shot Rick! I think I like exploring the background in the pics you guys take as much as the object at the center of attention. The background in the revised pic seems is a little dark on my monitor, but the galaxy is nicer.

[gvanhau]

Beautifull image Rick.

Pity you didn't have the best seeing conditios, but so is this hobby...

Geert

[Rex]

Nice repro Rick, like Kevin, I like to search the back ground of these really deep images, so many things to look at.

[RickS]

Ta, Mike. I'm of two minds myself. I don't like the flat look you get from too much dynamic range compression although it does bring out more detail.



Thanks, Allan. I didn't draw any masks :) I may play around a bit more although I'm not sure the data is good enough to justify a lot more effort.



Thanks, Kevin. I thought it looked a bit darker too although I didn't do any processing that should have caused that. I even measured a section of background and the stats were the same between old and new. Might have to check again when I get home to the data. I might have been tired and made a mistake...



Thanks, Geert. Unfortunately, we have to do the best with the data we get!



Thanks, Rex.

[Rod771]

Nice image Rick! :thumbsup:

I prefer the repo, a touch more contrast in the main object. Don't you just love it when you can't decide between two versions of an image, it happens to me all the time. :rolleyes:

[RickS]

Thanks, Rod!

[SamD]

Very impressive depth and resolution on the galaxy !

I've used the image for some catalog testing ...

From the Hubble Guide Star Catalog II, stars with VMag 21 (the catalog limit) are easily visible. I reckon you have stars to about VMag 22.5.

There's also about 100 galaxies from the Principal Galaxies Catalogue. The faint one PGC3169353 top left (red square) has a radial velocity of 77,000 km/s, putting it about 3.7 billion light years away.

Like the microquasar you mentioned, there's bound to all sorts of other interesting things in there.

[RickS]

Thanks very much, Sam! What did you use to do the annotation?

[RickS]

Final (???) tweak here: http://www.astrobin.com/133431/C/

In the second version I managed to clip the background so I have restored it to it's original glory while maintaining a bit more contrast on NGC 7793 itself.

Cheers,
Rick.

[marc4darkskies]

Ah ha! Sorry I missed this! I wouldn't have used wavelets but yes, that's definitely what I had in mind! More structure visible and it no longer looks, well, over exposed! :) Nice! :thumbsup:

[RickS]

Thanks, Marcus. Although I used a chisel instead of a screwdriver I was hoping that was what you were thinking :)

Cheers,
Rick.

[Ross G]

A beautiful galaxy photo Rick.

I love the colours and detail.

So sharp.

Ross.

[SamD]

It's some code I've cobbled together over the last couple of years (in C#). I use a local copy of the Principal Galaxies Catalogue, but the program queries the GSC-II catalog online on demand (it's about a billion stars so it's too large to download entirely).

I was wondering what sky brightness you had when imaging to get the very dim limiting magnitude ?

[RickS]

Thanks, Ross.



Nice work! I used the PI annotation script and it noted PGC687110 but not PGC3169353.

One night out of five was at a pretty dark site (Glen Aplin.) The other nights were at Hazeldean and Ten Chain Hill which aren't far from civilisation and aren't exceptionally dark.

[SamD]

Not sure about the PI annotation script, I thought it would have grabbed all the galaxies from the PGC. Maybe the smaller galaxy is not displayed because it's so close to the much brighter PGC687110, or maybe there's a magnitude threshold ?

If you use your image RA and Dec bounds and query the PGC directly you get about 120 galaxies in total:
http://leda.univ-lyon1.fr/leda/fullsql.html

select * where al2000 > 23.93833 and al2000 < 23.99278 and de2000 < -32.2967 and de2000 > -32.9361 and objtype='G'

Also the fairly dark sites match my recent calculations on CCD Limiting Magnitude. When I put your equipment and exposure times into my spreadsheet I get a stellar VMag limit of about 22.4 (with 21 VMags/arcsecs2 skies), vs 21.9 (with 20 VMags/arcsec2), and 22.9 with 22 VMags/arcsec2.

[RickS]

Sam,



It's the PGC Hyperleda I catalog. No options for magnitude. You can add new catalogs but I haven't have the time or inclination to play with it further.



Thanks for the pointer. It has been more than a decade since I last formulated a SQL query but I could probably manage that :)



Do you have a model for magnitude limit for an extended source? I still like to think I captured jet R4 of NGC 1097 at 27.6 mag/arcsec^2. All that data was from very dark sites...

[SamD]

From say 22 mag/arcsec^2 dark skies at zenith, at F/9, with 9 micron pixels, and say 14hrs on Luminance, I reckon a 27.6 jet is believable ! (As well as an awesome effort !)

On my calculations, a 27.6 mag/arcsec^2 jet should have come out on the image with a SNR of 0.8. This isn't really enough for stellar sources, but, with only moderate stretching and noise reduction, is definitely discernible for something like an extended jet.

[RickS]

Thanks very much for the model (and kind comments) Sam. I'll dig into this some more as it is very interesting to me. Shiraz/Ray has been doing some very interesting work in this area. I'll drop him a note...

Cheers,
Rick.

[gregbradley]

That's the best 7793 I've seen Rick. Very nicely done.

Greg.

[RickS]

Thanks, Greg!

[Andre27]

One of the best I have seen , well done,love those background galaxies.

[RickS]

Thanks, Andre.

[Leonardo70]

Very Nice Rick. Love the contrast.

All the best,
Leo

[RickS]

Thanks, Leo.

[Geoff45]

Nicely done Rick. Having done this one myself I know that it's quite a difficult one to process--getting right down to the small almost pointlike central core and still getting detail in the fainter outer regions doesn't come easy.
Geoff

[RickS]

Thanks, Geoff. It was a difficult one and I'm sure that a repro will improve it one day. Perhaps with some more/better data too.

[SimmoW]

How did I miss this magically deep image?! Gorgeous Rick, sets us all in our place in the universe.

[RickS]

Thanks, Simon!