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16.5 hours on the Draco Dwarf.

ollypenrice

By ollypenrice
in Imaging - Deep Sky

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ollypenrice

ollypenrice

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Thanks to Knight of Clear Skies for the suggestion that this might be interesting. It was. Firstly I took a lot of persuading that the open cluster-like powder of tiny stars in the centre really was a dwarf galaxy at 81 kiloparsecs.I think it is, though. It was nice, also, to catch a fair amount of patchy IFN including that distinctive streak. I haven't seen this in images I've found but doubtless someone will have caught it before. I really needed good flats for this and finally obtained some for Yves' SXVH36 by shooting them in AstroArt rather than Nebulosity. Flats shot in Nebulosity always over corrected but, at long last, that problem is solved.

So this took two nights in the tandem Tak. SQM 21.75 and superb seeing. Atik 11000, 14x10 minutes per colour. SXVH36 19x30 minutes luminance. Total 16.5 hours. Processing in AstroArt, Registar, Pixinsight and Photoshop CS3.

For the fullsize (good for fuzzies) click on the image and there should be a button in the bottom left.

Draco%20Dwarf%2016point5%20Hrs.jpg

Olly

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Knight of Clear Skies

Knight of Clear Skies

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Great stuff, looks fantastic with the IFN snaking across. Zoom right out and the dwarf turns into a background glow.

I've been reading up on the Draco Dwarf since I had a quick go at imaging it myself. Here's a plate from the 200" Hale scope with a large number of RR Lyrae variables identified, used to estimate its distance. Same orientation as Olly's image so it's easy to match up a large number of them, and there are even a few in my lens image. Walter Baade is credited as a posthumous co-author of the paper it's taken from.

Also found this paper on the star counts used to determine the shape and size of the dwarf. I haven't attempted to read it properly but have successfully eyeballed the diagrams. ;)

Also of note is a nearby mag 19.6 quasar [VV2006] J172257.0+581110 at 8 billion light years distance.

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Martin Meredith

Martin Meredith

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That's a wonderful image Olly, and very useful for future identification purposes. A most unusual sight, reminiscent of a bright OC superimposed on the Milky Way, and to think that it is something else entirely is amazing. I'm looking forward now to having another go with the Lodestar to see how many of the little blighters I can detect as live stacking progresses. The individual members must be around mag 20 or fainter.

Knight, thanks for the resources.

Here's a paper with Draco Dwarf photometry results; there fig 11 shows the colour vs magnitude plot for likely dwarf members, suggesting a smattering from mag 16 (R) and fainter, with the bulk around mag 22-23 (R), with V mags about 0.5 mag fainter for many stars.

Martin

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ollypenrice

ollypenrice

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1 hour ago, PhotoGav said:

Yup, that works! Stunningly tight stars Mr. Penrice. Do you attribute that to filters, optics, processing or simply a combination of everything?!

 

I stretched the luminance under a star mask at first, though I always remove the mask once the image is about one third stretched since it soon creates artefacts. Once I started to stretch very hard in search of the IFN I kept a less stretched bottom layer and took off the haloes the hard stretch was throwing up. Both transparency and seeing were particularly good on the two nights of capture, which helped. For star colour I just selected the stars, increased saturation and then ran Noel's Increase Star Colour. I prefer doing that to running two instances of the Action.

Olly

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PhotoGav

PhotoGav

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9 minutes ago, ollypenrice said:

I stretched the luminance under a star mask at first, though I always remove the mask once the image is about one third stretched since it soon creates artefacts. Once I started to stretch very hard in search of the IFN I kept a less stretched bottom layer and took off the haloes the hard stretch was throwing up. Both transparency and seeing were particularly good on the two nights of capture, which helped. For star colour I just selected the stars, increased saturation and then ran Noel's Increase Star Colour. I prefer doing that to running two instances of the Action.

Olly

Thanks for that Olly - it certainly worked!

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opticalpath

opticalpath

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Wow, what an eyeful :shocked:.   Superb, Olly.

Adrian

(BTW, and this is really being hyper-critical .... is that just a wee bit of curvature or rotation creeping in to the left side of the image?  Only visible when pixel-peeping the full res. version)

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ollypenrice

ollypenrice

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55 minutes ago, opticalpath said:

Wow, what an eyeful :shocked:.   Superb, Olly.

Adrian

(BTW, and this is really being hyper-critical .... is that just a wee bit of curvature or rotation creeping in to the left side of the image?  Only visible when pixel-peeping the full res. version)

Yes, you're right. Looks like a bit of field rotation. I hadn't noticed it but the 30 minute subs are unforgiving. I'll re-do the polar alignment when I get a quiet night.

Olly

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opticalpath

opticalpath

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1 hour ago, ollypenrice said:

....... Looks like a bit of field rotation. I hadn't noticed it but the 30 minute subs are unforgiving ......

Olly

 

Very true, especially so with such a wide FOV .... or is it just pixel scale that matters for sensitivity to field rotation?  I can't work it out. Probably both. 

When I was starting the 'headphones' project, I considered doing 60 minute Ha subs.  I might have got away with it but I chickened out!  (Think of the darks :shocked:)
This was a test shot - a single one-hour sub at 1.1 arcsec per px, calibrated and stretched a bit: http://universalconstant.com/PK-164-001H3600.jpg
 

Adrian

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ollypenrice

ollypenrice

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16 hours ago, opticalpath said:

 

Very true, especially so with such a wide FOV .... or is it just pixel scale that matters for sensitivity to field rotation?  I can't work it out. Probably both. 

When I was starting the 'headphones' project, I considered doing 60 minute Ha subs.  I might have got away with it but I chickened out!  (Think of the darks :shocked:)
This was a test shot - a single one-hour sub at 1.1 arcsec per px, calibrated and stretched a bit: http://universalconstant.com/PK-164-001H3600.jpg
 

Adrian

I think it's FOV. If your guide star is on-axis, as is the case for our rig, the image will rotate around that and the further off axis you go the worse the effect.

Olly

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Uranium235

Uranium235

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Looks great Olly! Might be worth doing a WCS solve and annote to see what else you've detected :)

Did a little pixel peeping too (as always!), not sure whats happened in the top left corner but I'll take that as a one-off ;)

 

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