9 replies to this topic

[Rick J]

I'm jumping out of order here.  Normally I post in order taken (FIFO) which means I'm processing and posting February images.  But I took an image in late May trying the "impossible".  Likely needing more data I processed it last night to see if I'd caught anything.  Turned out a surprising success.  I'm posting this while it is still in the sky for those who, like me, push the envelope of what amateur imaging can accomplish.  First some background.

As most know by now I like to go where most amateurs fear to tread.  Back in the fall of 2008 it was announced that a Dutch school teacher, Hanny van Arkel, looking at Galaxy Zoo images saw something odd.  Hundreds had looked at the same image before her but she was the only one to wonder "What's that?" and post the question.  It turned out to be a green object outside the obscure galaxy, IC 2497.  It was bright green though on the Sloan images it was blue.  At the time it was a mystery.  Fortunately the moon was out of the sky and it was well placed so I gave it a try to see if I could pull it out.  Digital imaging was still new to me and I wanted to test its limits.  It turned out to be relatively easy, not a difficult test after all.  Still it became the first amateur image of it as far as I and Hanny could determine.  A check of Google images fails to turn up an amateur image of it even now.  Though it misses many posted to Flickr and the like.  Still it surprises me a unique but rather easily imaged object is so ignored by most amateur imagers.  It was later determined to be a cloud of mostly ionized oxygen illuminated by a now faded QSO in the heart of the galaxy, possibly left over from something IC 2497 digested.  Were there others?  Galaxies devour their kind constantly so it seemed likely.  

Back in April, 2015 the HST group announced they had found similar objects lit by a few other galaxies now vanished quasars so it wasn't unique after all, just very rare.  One of their discoveries, NGC 5972, was well placed in my sky in late May so I had to give it a try.  Like Hanny's Voorwerp (voorwerp is Dutch for "object") these are green.  Due to late may skies allowing me only time for one of my typical 100 minute image runs in dark skies I took one round of data on it.  I expected more would be needed as this is much fainter than Hanny's Voorwerp.  I was wrong.  I may not have HST resolution but much of the green object is seen. Yet again it wasn't as difficult as I expected.

It is thought these are gas clouds lit by light echos of long faded quasars in the heart of these galaxies.  I am guessing they are blue in the Sloan image because those include ultraviolet mapped to deep blue along with blue mapped to a lighter blue.  This Uv light may be stronger than the green or blue causing the color shift.  In my pure LRGB image the green is the natural result even after I subtract green from air glow I have in my images. The green is apparently due to OIII shifted by cosmological redshift from its normal teal to green.  The shift is too great to allow standard OIII filters to be used on these so I've not attempted that.
 
You can read more about these Voorwerpjes (Dutch for "objects" "small objects") at http://www.skyandtel...past-042215234/

Redshift puts the galaxy about 410 million light-years distant.  HST data says a 40" filament is 75,000 light-years long at the distance to NGC 5972.  That works out to a distance of just under 390 million light-years. A rather good agreement as these distances go.  Using the HST distance I get a size of 166,000 light-years for the galaxy including the small puff of green just south of the galaxy.  The galaxy was discovered by Édouard Stephan on June 29, 1880.  It is listed as S0-a or S0/a depending on the source.

For those new to my posts I'm including my November 2008 image of Hanny's Voorwerp.  It isn't nearly as impossible as most seem to think it to be.

14" LX200R @ f/10, L=4x10' RGB=2x10', STL-11000XM, Paramount ME

 

NGC 5972 full image at 1" per pixel

 

NGC 5972 Annotated

 

Hanny's Voorwerp from 2008 at 0.5" per pixel

 

Attached cropped image of NGC 5972 at 0.67" per pixel.

Rick

Attached Thumbnails

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Edited by Rick J, 16 June 2015 - 02:35 AM.

[bill w]

congrats on a great capture rick!

[lambermo]

Nice capture ! Also interesting to know that standard OIII filters won't catch these.

 

En nu hopen dat we nog vele andere voorwerpjes mogen zien

 

-- Hans

[HunterofPhotons]

 

 

En nu hopen dat we nog vele andere voorwerpjes mogen zien

 

-- Hans

 

My sentiments exactly, Hans.

Rick, your inquiring mind and lack of fear in treading where others have not gone are inspiring.

With apologies to Kermit, in astronomy "It's not common bein' green".

My best regards,

 

dan k.

[Rick J]

I hope this gives some out there with 8" and larger scopes the incentive to give this one or others with these ghostly echos a try.  I tried one other so far but on a far worse night.  Still I think something came through.  Several are still high enough to give it a go.  Those with 17" and larger scopes should find several of these surprisingly easy.

 

I'm beginning to not like the title I gave this post.  Voorwerpjes is just Dutch for objects small objects and of course all amateur imagers take objects though small is relative in astronomy I suppose. Somehow English as taken the Dutch word and given it its own meaning.  Somehow that bothers a part of my brain. 

 

I haven't checked other galaxies with these light echos for redshift.  A 12nm OIII filter should work for those with a redshift of less than .00914.  That's a distance of about 125 million light-years.  This one is over 400 million light-years distant so over 3 times further away than any OIII filter I know of can reach.  I don't even own an OIII filter but can borrow a 6nm one (old Astrodon series 1 filter) but that's good only out 60 million light-years or so and none are that close that I know of.  I wonder how the HST does it?  Someone suggested a Sloan G filter might work better than a standard green filter.  I don't know its charateristics.  If someone has one you might give it a try.  I saw one claim it helped to see Hanny's Voorwerp visually in a very large light bucket.

 

Rick

Edited by Rick J, 16 June 2015 - 02:40 AM.

[Magellanico]

NGC5972 is faint and difficult. Thank you for sharing these images. Good job.

[Rick J]

I've heard from a Dutch amateur who tells me the sites I saw saying Voorwerpjes means objects are not correct.  The correct translation doesn't exist in English but if it did it would be "objectlets".  In other words small objects.  Indeed that's what Google translate would have told me if I'd have checked.  I usually try to check things but when several sites said the same thing I didn't do so.  That will teach me!  According to Google translate "voorwerpen" is the plural form for voorwerp.  Seems a better choice since these clouds are tens of thousands of light-years across.

 

Rick

Edited by Rick J, 16 June 2015 - 03:03 AM.

[lambermo]

I agree, I would describe 'voorwerpjes' as '(multiple) small objects'. 'voorwerp' to 'object' or even 'that what has the attention', 'voorwerpje' to 'small object' and with an extra s appended it's multiple small objects. Multiple (not small) objects translate to 'voorwerpen'.

 

I see two small green areas next to NGC 5972, so voorwerpjes describes it perfectly for me

 

-- Hans

[Joepie]

Great image again Rick! It didn't occur to me that redshifted OIII would look green. I'll be more careful next time when processing galaxies and avoid using hlvg Did you tell Hanny about this picture yet? She might publish it on her website if you do

[Rick J]

I think the reason it is green for me at least is I use Astrodon series 2 filters which overlap slightly at the OIII lines to help show the line color correctly but when shifted by nearly 20nm it is now fully in the green filter so comes out bright green.  Sloan uses different filters and sees it still as blue.  More an aspect of filters used than real color.  Spectral line color isn't a strong point of RGB filters that tend to see it as all one color.

 

Without thinking I did apply the HLVG filter and it turned these areas very dark.  They really stood out when looking at the image before merging with the luminance.  Again a result of how our RGB filters work with line spectral features.  I had to go back to my old ways of dealing with the severe green air glow I get here at least for the region around the galaxy.

 

These however aren't pure line features more of a florescence so broader but still quite narrow band features.

 

No I've not contacted Hanny.  When I took her voorwerp in 2008 word got back to her by many who saw it.  So she contacted me.  I suppose I should return the favor.  I tried for a couple others but my sky conditions were horrid and I got so much noise I doubt I got anything real.  Most will be too far west once my skies clear and the moon is out of the way so I'll have to wait until they come around again.

 

Rick