Sculptor semidwarf NGC 7793

[Placidus]

NGC 7793, a semidwarf galaxy in Sculptor.

The thumbnail is strongly cropped. The (revised, more data) full image is here (https://photos.smugmug.com/Category/Astrophotography-at-Placidus/i-7ZQ4msK/0/O/E%20NGC%207793%20Trish%20Blend.jpg) .

Taking the shot: We found this a bit difficult because there are only the most feeble of guide stars in the field if the galaxy is centred. On one night, we used those feeble stars and managed after a fashion. On the other two nights, we offset things a bit. Curiously, having a good guide star and three feeble ones was not hugely better (0.65 sec rms guide error) than just three feeble ones (0.75 sec rms), unimportant against 2.2 sec arc seeing, so we could perhaps have centred the galaxy after all.

What we saw: There are no obvious dust lanes here. Perhaps semi-dwarfs are tidy creatures. But there are some flocculent M83-style spiral arms with clumps of bright blue stars, and a nice salmon-pink centre of older stars. The whole effect seems almost three dimensional and rather pretty.

Squillions of small galaxies in the background, including a magnificent pair of interacting tadpoles at the left edge about 10 o'clock, and many other near face-on fellows 'with form' as the Bill would say.

Because of our indecision about where to point, there is no colour data for the extreme right hand edge, but we didn't crop it off because there's a cute galaxy there that we'd like to revisit.

Image details: Field 38' arc, 0.55"/pixel. North to the left. Lum 16 hours (1hr unbinned subs), RGB 2 hrs each (30 min 2x2). Aspen CG16M on 20" PlaneWave. Processing using GoodLook 64.

At last, after at least 120 mm of rain this month, three nights of imaging. The twitching and the craving subsides a little bit.

Cheers,
Mike n Trish


Edit:

Also attached is 3hrs in H-alpha (3x1hr unbinned), with the position of the microquasar (mentioned by Rick) marked with an arrow.

Further edit:

We acquired another 2.5 hours of RGB in each channel, for a total of 4.5 hours per channel, and reprocessed.

[RickS]

Lovely image, M&T, and a good bit better than my 2014 rendition. There's a microquasar at 07:30 - the red bit in amongst the pink.

Cheers,
Rick.

[Atmos]

Very nice result with some fascinating smaller galaxies. The galaxy on the right hand edge, go for it! Looks quite interesting, reminiscent of a tiny NGC 300 :)

[billdan]

That looks really good M&T, love the colours you have captured and heaps of different syles of galaxies. The question mark asterism above the galaxy looks cute as well.

Cheers
Bill

[Geoff45]

Nice good detail and colour there guys. You describe it as a semidwarf. Any idea of the real size compared with (say) the Milky Way?

[Placidus]

Thanks muchly, Rick! Huge thanks for drawing our attention to the microquasar.

We found the microquasar on a Chandra image in x-ray (http://chandra.harvard.edu/photo/2010/ngc7793/). Looks nothing like the LRGB image. Luckily, we'd also done 3 hours in H-alpha (see thumbnail), and that looked exactly like the Chandra image ! In either x-ray or H-alpha, the galaxy is only about 2/3 the size that it is in LRGB.

The microquasar and it's associated jets is the structure elongated along the 10 o'clock 4 o'clock direction, labelled with an arrow. It is noticeably brighter in H-alpha toward the 4 o'clock end.

[Placidus]

Thanks, Colin!



Thanks, Bill. Yes, the star field is quite pretty.



Hi, Geoff. Wikipedia gives it 9.3 min arc at a distance of 12.7 MLY, which would make it 34 KLY across. That makes it somewhere between the LMC at 14 KLY and the Milky Way at 100 KLY.

Have a peek at the H-alpha thumbnail also! :)

Best,
Mike

[RickS]

Very cool, guys!

[Stevec35]

Nicely done M&T. I did this one a while back and also had a lot of trouble with guide stars. Perhaps that's why you don't see a lot of images of it. I've never heard of the term semi dwarf before. I thought that these galaxies were usually called flocculent spirals.

Cheers

Steve

[Peter Ward]

Humm....some minor aberration/artifact quibbles ....but oh, what an sublimely interesting result !

This is the sort of stuff I really like to see...the amour in amateur astronomy

Yep.

Like it.

A lot. :thumbsup::thumbsup:

[SimmoW]

Lovely Team, a humbling image with all those galaxies surrounding.

Just one random crop attached looks rather Hubble-like!

[gregbradley]

Excellent image Mike.

Greg.

[strongmanmike]

Wow check that out :eyepop:, so colourful...(shame you can't see it all Mike :sadeyes:), like you Mike I love all the tiny background galaxies as much as the main target :thumbsup: Love the Ha-only shot too, it's not until you do this that you realise just how extensive the star forming regions actually are in most galaxies

Another great job guys, enjoyed the view and great job pointing out the micro quasar too :thumbsup:

Mike

[Slawomir]

Wow, truly wonderful image, beautiful work M&T :thumbsup:

[Placidus]

:) Thanks again for pointing it out.



Aye, can't remember where I saw it referred to as a semi-dwarf. Perhaps it's not a technical term, but it does get used a bit.



Thanks muchly, Peter. Our camera does seem to produce a goodly crop of bright blobs that aren't in the sky. Perhaps next camera might be one of these low noise CMOS beasties. Sticking with the Apogee because I know how to write software to control it.



Thanks, Simon. Far from the milky way, almost any random patch of sky seems full of interesting stuff, but the seeing has to be upper decent to tell the smallest ones from stars.



Thanks Mike! You are most encouraging. (We needed that after all the rain). Trish did the final colour on this one. My own attempt had amusing turquoise stars. After Rick suggested I look for it, I couldn't find the microquasar in the LRGB image, but it was easy-peasy in H-alpha.



Hi, Slawomir! Very glad you like it.

Hunting around for other images. We knew of excellent (and sharp) shots by Strong Mike and Rick. Just found this (https://www.flickr.com/photos/14298125@N08/27388513644/) by Warren Keller, taken at SSRO in New Mexico. It confirms that a lot of the orange blobby things immediately toward 11, 12, and 1 o'clock of the main galaxy are indeed other very distant galaxies. Ah, to have a modern, leak-proof rat-free ship like that.

[atalas]

Good work M&T.

[Adso]

Stunning photos! :-)

[multiweb]

Looks terrific Mike. Super deep and very colorful. So many faint fuzzies around. :thumbsup::thumbsup::thumbsup:

[Placidus]

Thanks guys, much appreciated. :)

[topheart]

Excellent work M+T !!

Cheers,
Tim

[alpal]

Great Pic - Mike & Trish,
improvements? -
maybe add a bit of non-global contrast with a blurred layer mask just to the core?

cheers
Allan

[Placidus]

Thanks, Tim.




A good suggestion, Allan. The existing processing of the core was designed to show off the quite stellar (even pin-prick) centre, which would indicate a very active galactic nucleus. I was so pleased with that, I didn't look so hard a bit further out.

Best,
Mike

[alpal]

Hi Mike,
Fair enough,
I would have had a go myself but
I didn't dare touch the picture of the master. :)

cheers
Allan

[stevous67]

This is a stunning result Mike and Trish, I've really enjoyed scanning through your image, with the saturation being just to my liking.

Regards,

Steve

[marc4darkskies]

You guys are pumping out some very cool galaxy shots M&T! :thumbsup: Very nicely done and great field to wade around in!

Cheers, Marcus

[Placidus]

Thanks, Steve! We puzzle about how saturated to make the image. I'm somewhat of the view that colour tells you about the astrophysics - blue stars are hot and therefore young, pink patches are HII, etc, and since most star clusters are predominantly blue-white, if you see a bunch of orange blobs, they're likely to be distant elliptical galaxies rather than a very funny coloured open cluster just round the corner. So colour is good.



Thanks heaps Marcus. We were blessed with three nights of actual clear sky close to the full moon, and only one technical screw-up (where I checked to see what time the moon rose, and thereby accidentally changed the night's script to photograph the moon once it was up, when I meant to switch to photographing the galaxy in H-alpha !!! Only lost a single frame, but it was pretty embarrassing.)

[Placidus]

There's not a lot in it, but we've added another 2.5 hours of colour per channel, fixing the colour in the missing right margin, and reprocessed. We think the colour balance is slightly better (less magenta), the core is slightly sharper, and the dust lanes in the core are now evident.

New image here
(https://photos.smugmug.com/Category/Astrophotography-at-Placidus/i-7ZQ4msK/0/O/E%20NGC%207793%20Trish%20Blend.jpg)

[Spookyer]

Great work

[strongmanmike]

Nice touch up guys :thumbsup:

Mike

[RickS]

:thumbsup:

[strongmanmike]

:lol:....even the very smartest and most capable among us...can be a little stupid on ocasssion :)

Mike

[Placidus]

Ta, Brett.



Thanks, Mike.



:)



Guilty as charged. :scared3:

[Andy01]

Crackerjack image guys, up there with the best on show here, well done :)

[Placidus]

Thanks, Andy, that's most kind.