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Hickson 44 galaxies and a missing asteroid


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Hi all,

Something's doing my head in.

First up, this is my attempt at the Hickson 44 group of galaxies in Leo from last night: NGC 3193, 3190, 3187 and 3185. I'm reasonably pleased with it given their small size and my limited imaging capabilities. This is the full frame and a crop of the image.

35 x 5 min exposures, ISO800, unmodded Canon 450d, 250mm f/4.8 Newtonian, stacked in DeepSkyStacker and processed in Photoshop.



I selected that galaxy group for imaging last night because I knew that Asteroid (727) Nipponia was passing through the group, and I like imaging asteroids particularly if they're in the same FOV as other objects. What's doing my head in is that the asteroid just isn't there. I scratched my head about this for ages, and then it dawned on me that because the asteroid is in a slightly different position in each frame, DSS seems to remove it as it 'thinks' it is some sort of optical artifact or defect. Sure enough, I checked the original frames and Nipponia is there all right, but not in the final stacked image.

How can I get DSS to keep it in the image (even if it does result in the asteroid being a line rather than a point)? I could do a 'comet-centred' stack but that would just result in the stars becoming streaks, with a little dot for the asteroid, and it would look a mess.

Edited by lukebl
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As an update, I've now done a little animation of Asteroid Nipponia passing by the group, using the 35 frames I used in the above result. As you can see, the sky transparency worsened considerably toward the end of the sequence. This shows the movement in about 2h 50m.

Unless my maths is hopelessly out, I calculate that the asteroid is over two million million times closer than the galaxies. Well, that just about puts it all into perspective!


Edited by lukebl
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That's very cool.

As for your processing issue how about producing the image in two passes? The first for the background (let the asteroid get removed) and the second for the asteroid alone. When doing the asteroid pass don't worry that the background gets messed up, just build a mask when you combine the two image passes.

I'm not a DSS user and I tend to write my own processing software, so my advice may be a bit overcomplicated. I don't know if any of the off-the-shelf programmes have an easier way to do this. I know PixInsight has processing masks, but I don't know how that applies to stacking.


Edited by jwr
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great pics! :D

How did you make the animated pic, btw? Would love to make those also. Very good for seeing small changes and seeing condition changes over time. :p

Thanks for the comments, guys.

I did the animation in Photoshop and exported it as a gif. It was fun but VERY fiddly. I opened up each of the 35 frames, pasted them into one image, played around with the alignment of each frame till they were as close as possible, cropped the image so that it was a manageable size, then exported it. With 35 frames you get quite a nice smooth animation. It's handy that most asteroids move quite a bit in a couple of hours.

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Many thanks, all. It was mounted on an NEQ6.

Mike, I tried the 'comet stacking' in DSS, but it looked a mess. Never seems to work for me. Never mind, though. I'm quite pleased how the galaxy group came out.

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