NGC 7424 is a starburst grand spiral in Grus. We call it Chopin, on the grounds that it looks like a frenetic set of fingers playing an arpeggio on the keyboard.
T'was a real challenge to get a half-decent image, as the surface brightness is only 15 mag/sq arc min, a full magnitude fainter than the Pavo spiral for example. The brilliant orange star (in the full image, not the crop) at right is only mag 7.
Perhaps the thing of most interest is the huge number of pinpoint bright blue OB regions in the multiple spiral arms. As seems typical of Grus, there are squillions of tiny galaxies in the background, including edge-on spirals, and lots of orange ellipticals, often in clusters.
In our image, the small central bar has a bit of decon artifact around it, and is a bit more orange than in the stunning, jaw-dropping, SSRO image, but we'd have to stand on tip-toe to reach 2.2 km altitude.
Lum: 15 hrs in 1hr subs. RGB: total of 9 hrs in 30 min 2x2 binned subs. Aspen CG16M on 20" PlaneWave on MI-750 fork. New moon. Field 35' across.
You did great there. I tried imaging that last year and it was too faint for anything other than nice dark skies.
A strange looking galaxy. Its obviously distorted but I can't see the orbiting companion galaxy. I wonder if its on the other side of it so we can't see it.
1 hour subs. Wow, how do you find those? I guess you are getting way above the noise floor but you'd have to have great confidence in your tracking. The stars look a bit hazy, perhaps a consequence of such long subs, the PE averages out to round stars. No free lunches I guess. Would you recommend 1 hour subs?
You did great there. I tried imaging that last year and it was too faint for anything other than nice dark skies.
A strange looking galaxy. Its obviously distorted but I can't see the orbiting companion galaxy. I wonder if its on the other side of it so we can't see it.
1 hour subs. Wow, how do you find those? I guess you are getting way above the noise floor but you'd have to have great confidence in your tracking. The stars look a bit hazy, perhaps a consequence of such long subs, the PE averages out to round stars. No free lunches I guess. Would you recommend 1 hour subs?
Greg.
Thanks, Greg! Yes, something must have triggered all that star formation, but there is no obvious guilty party.
1-hour subs: We'd definitely recommend them for really ultra-faint stuff, but not for middling to bright stuff.
Tracking: We had to modify the worm drive on the MI-750, which as shipped was really a visual mount. We replaced the servo-motors with ones with three times higher gearing. We added push-down bearings to stop the worm from climbing up the face of the main bronze gear. Factor of 10 improvement.
Guiding: We routinely use two guide scopes and multiple guide stars. The fast guider is a cooled camera on an ED80, and uses 1 sec subs with typically 3 to 10 guide stars. The slow guider is off-axis, again cooled, and takes 10 sec subs, typically using perhaps 20 guide stars. In the milky way, RMS guiding error is typically about 0.3 sec arc. But for NGC 7424, out in the dark wilds of Grus, we had only a few faint guide stars, and RMS error was more like 0.6 sec arc.
Cracking data collection there Mike and Trish. Smooth image with good detail. Colour is nice in the galaxy. Star forming regions look cool and like you say heaps of galaxies in the back ground. Well done.
There is some odd red dots in the image though. One in the actual galaxy and one just to the upper right of it.
Cracking data collection there Mike and Trish. Smooth image with good detail. Colour is nice in the galaxy. Star forming regions look cool and like you say heaps of galaxies in the back ground. Well done.
There is some odd red dots in the image though. One in the actual galaxy and one just to the upper right of it.
Overall another interesting image. 1 hours subs.
Thanks, Paul!
Finally figured out what those red blobs are. They plagued the Yoda image (resolved with lots of H-alpha), and now this. There were some tiny nano-bits of translucent spludge (spider slime or something repulsive) on the red filter, and starlight was illuminating them. Even though the translucent blobs were fixed on the filter, and we move the camera by many pixels between shots, the red blobs moved with mostly with the stars, not the chip. That meant it took a long time for us to suspect the filters.
The camera + filter wheel + guider weighs about 10 kg, was 2.5 metres up in the air, comes off as a single unit (after undoing 4 bolts), and is at an awkward angle, discouraging safe removal. Yesterday we positioned the scope to be pointing at the zenith, made a giant stand to go under the camera combo, removed, disassembled and cleaned the filter set. Found the main blob and some others. We could see more dust landing on it, even while we worked. But now we understand what was causing it, and have a system, we should have less trouble in future.
I fear the magnitude of this stunning result will be lost on many, ( Chopin in the title..,and "top of the pops" are unlikely to meet . ) but I am
gob smacked by the sheer depth and quality of this image.
The camera + filter wheel + guider weighs about 10 kg, was 2.5 metres up in the air, comes off as a single unit (after undoing 4 bolts), and is at an awkward angle, discouraging safe removal. Yesterday we positioned the scope to be pointing at the zenith, made a giant stand to go under the camera combo, removed, disassembled and cleaned the filter set. Found the main blob and some others. We could see more dust landing on it, even while we worked. But now we understand what was causing it, and have a system, we should have less trouble in future.
Great result guys, a lovely image of this galaxy, a few warts but meah you like using only your own software so se la vi, still a fantastic image I recon The lovely image scale always makes it a treat for us lower image scale plebs
Nice work on a very tricky target, M&T! I spent quite a few hours on it at Astrofest a couple of years back so I know
Glad you got the red blobs sorted.
Cheers,
Rick.
Thanks muchly, Rick.
Quote:
Originally Posted by sjastro
Very fine image Mike & Trish.
Regards
Steven
Cheers, Steven.
Quote:
Originally Posted by Atmos
Very nice Grand Spiral galaxy
Quote:
Originally Posted by Peter Ward
I fear the magnitude of this stunning result will be lost on many, ( Chopin in the title..,and "top of the pops" are unlikely to meet . ) but I am
gob smacked by the sheer depth and quality of this image.
Seriously impressive stuff
Thanks, Peter. We're seriously encouraged.
Quote:
Originally Posted by gregbradley
That's phenomenal guiding accuracy. I thought I was doing brilliantly with .62 to 1.05 arc second. Average about .9.
Greg.
Thanks Greg. The use of multiple guide stars and dual guiders really helps.
Great result guys, a lovely image of this galaxy, a few warts but meah you like using only your own software so se la vi, still a fantastic image I recon The lovely image scale always makes it a treat for us lower image scale plebs
Mike
Hi, Mike,
That Palomar realuminizing video link was right on the mark. That's exactly how it felt. Thanks!
A fine image M&T! Alas those red splotches detract but can be processed out. I also notice a reddish annular gradient over the frame(?).
Hi, Marcus,
The reddish annular gradient is almost certainly due to our lousy flats. Trish just read the AS&T article on flats, and emailed optec to ask about their precision flat system - a giant electroluminescent panel that bolts permanently to the dome. In the past we've found that EL panels have holes in their spectrum and don't work with 3nM filters, but hopefully these guys know what they're doing. Santa may have something for us.
A stunning galaxy Mike and Trish. The field of view is dotted with smaller galaxies as we scan around at 100%. A nice warm glow from the bright star in the image.
R
Hi!,
A galaxy that will not go up never on my horizon but unfortunately very beautiful! I agree with what Paul wrote on the management of H alpha but in general a very good image. But I just can not see the fingers of Chopin, although I have a diploma in piano :-)
Cheers,
Fabiomax
A stunning galaxy Mike and Trish. The field of view is dotted with smaller galaxies as we scan around at 100%. A nice warm glow from the bright star in the image.
R
Thanks, Rodney. We puzzled about whether to crop off the bright star, but I think it adds more than it detracts.
Quote:
Originally Posted by Fabiomax
Hi!,
A galaxy that will not go up never on my horizon but unfortunately very beautiful! I agree with what Paul wrote on the management of H alpha but in general a very good image. But I just can not see the fingers of Chopin, although I have a diploma in piano :-)
Cheers,
Fabiomax
Thank you Fabiomassimo, we defer to your expertise. But the many individual spiral arms can (with averted imagination) be taken as at least metaphorically symbolic of flying fingers.
