View Full Version here: : Abell 42 - another planetary nebula halo
Stevec35
10-07-2016, 06:09 PM
Here's another object from the ongoing project to find planetary nebula halos. Abell 42 is already one of the faintest Abell planetary nebulae and of course the halo is even fainter. I wanted to get more data to flesh the image out a bit but the weather has been uncooperative lately to say the least.
Anyway here it is. Not what you would call spectacular.
Cheers
Steve
http://members.pcug.org.au/~stevec/Abell42_STXL6303_RC14.htm
Atmos
10-07-2016, 07:05 PM
When you start hitting some of the smaller planetary nebula without having a space telescope they do naturally start to become less "spectacular". It is a nice shot though, your 12" is going pretty deep to say the least. Nicely done Steve.
strongmanmike
10-07-2016, 11:00 PM
Well, certainly looks like a halo there Steve, is that a confirmation then?
Mike
Stevec35
10-07-2016, 11:23 PM
Well Sakib seems convinced. I was just having another look to make sure I didn't overdo my "halo brightening" processing. Possibly I did but there certainly something there.
Thanks Colin. It's actually a 14.5" but I imagine the 12" would produce similar results.
atalas
11-07-2016, 05:39 PM
Hi Steve
Man you do go after some tough ones!very cool object and so tiny...well done!.
Stevec35
11-07-2016, 11:46 PM
Thanks Louie. It's not that small and I have gone smaller but generally I don't image anything smaller than about 40". This was a request otherwise I probably wouldn't have bothered..
Paul Haese
12-07-2016, 09:39 AM
Looks like you got a halo on my screen Steve. Quite bright really too.
Stevec35
12-07-2016, 10:01 AM
Thanks Paul. It's artificially brightened a bit. Almost invisible on the unmodified data.
strongmanmike
12-07-2016, 10:31 AM
What do you mean by artificially brightened?
For the faint halos (http://www.pbase.com/strongmanmike2002/image/161295601/original)I have revealed, I create several versions where I have stretched the begeezus out of the faint data to varying degrees and then I (very) carefully blend just the faint stuff revealed, back into a more normally processed version, I then use targeted noise reduction on the layered in heavily stretched data to make it a bit smoother.....this is not artificial but more like enhanced. I think as long as the stretching done before the layering is done globally on the raw data and not "artificially" targeted by say, lassoing an arbitrary area, it is a valid representation, particularly for scientific purposes.
Mike
Stevec35
12-07-2016, 05:25 PM
Point taken. Artificial was a poor choice of words and enhanced would be more appropriate. I use a global stretching too followed by Jay Gabany's layered contrast stretching which seems to work okay but you have to be careful with it.
atalas
13-07-2016, 06:18 PM
Steve,Ive just moved up to 2000 mtrs from 380 mtr focal length....2.5' is tiny to me and probably most of us mate :)
Stevec35
13-07-2016, 10:49 PM
2000 mtr focal length - that sounds pretty long :). Point taken though - I've been working with long focal lengths for so long I sometimes forget.
strongmanmike
14-07-2016, 11:11 AM
Geezus Louie :eyepop: man!... you like big telescopes!! :rofl:
....or at least... you use several Powermates :question:
RickS
14-07-2016, 03:07 PM
Nice looking halo, Steve!
atalas
14-07-2016, 05:13 PM
:lol: Sorry Steve....yeah meant mm.
atalas
14-07-2016, 05:14 PM
:rofl: mines bigger than yours!I win.
Placidus
15-07-2016, 09:32 AM
Sure looks like a faint halo in your image.
In general, it must be very difficult to know for sure that it's a halo, and not an effect of dodgy flats (doesn't look it in your case), or of processing. As a very retired researcher, I'd be very nervous about any processing that did anything at all that was regionally selective - handled different parts of the image differently.
I could imagine that a formal way of doing this might be to move the beastie to a completely different part of the chip for each sub, register, and then use analysis of variance to see whether say the outer half of the halo region is statistically significantly brighter than the background. You'd need to use robust statistical methods such as a rank transform (most robust) or winsorization (more informative) to ignore stars.
Another vague concern is glare. One could perhaps analyze the glare pattern around a bright star and control for this using radial distance as a covariate. (No, I'm not volunteering. It's been too long).
Having said all that, it sure looks real from the foot of the bed. And it looks very beautiful too. Well done.
Best,
Mike
Stevec35
15-07-2016, 10:43 AM
Thanks Mike. You make very good points. My halo processing could no doubt be improved. It sounds as if Mike Sidonio has a better procedure. Basically I stretch the heck out of it and convince myself there is something there. Once I do that I use the more specific stretching procedures such as Jay Gabany's layered contrast stretching to bring out more detail. I also reprocess the image in subtly different ways and it's encouraging that they all come up with basically the same result. Sakib Rasool who is the coordinator of this exercise thinks I have this one pretty well right because it matches what he sees with extreme stretches of the DSS images. In general I think though that my skies are too bright for the really faint stuff.
Stevec35
15-07-2016, 10:43 AM
Yep - I assumed that
Stevec35
15-07-2016, 10:44 AM
Thanks Rick
strongmanmike
15-07-2016, 10:52 AM
All valid approaches Mike...but what Steve and I are essentially doing is simply identifying that something exists there and it's basic shape & extent. Interpreting it more accurately is for the pro's in the end as they have the large aperture telescopes, multi million dollar detectors and the dark steady sites necessary for this bit (ala my faint dwarf galaxy discovery) :)
I (and I imagine Steve) have a good understanding of my imaging system glare profile around bright and dim objects, I have stretched many, many objects looking for faint strange halos (and jets :lol:) so I know my system very well, if I suspect something I am pretty confident I have ruled out star glare, dodgy processing and flats. Perhaps though, when the faint halo is so faint and so uniform and so circular, such as with this one by Steve, it is indeed probably a little more difficult to rule out optical halation...? But I don't think the PN in this case is bright enough to cause the extent of what Steve has shown..?
All interesting discussion :thumbsup:
Mike
Stevec35
15-07-2016, 04:27 PM
Looking at my data again Mike there is unquestionably a halo there and it is round and symmetrical but very faint. My processing has probably made it more prominent than it actually is which I guess is not very scientific. In any case my STXL11002 has now returned from its enforced holiday in the USA so I will be taking a break from halos for a while.
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