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Sh 2-91, the Swan's other supernova remnant

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#1 Nightfall S Africa

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Posted 07 August 2017 - 04:17 PM

The meticulous S African observer Susan Young lives in the Kalahari Desert with her two dogs and two dobs. It's one of the worst places in the world to live—except for astronomers and meerkats, in which case it turns into one of the best places in the world.

 

Susan has posted three impressively detailed observing reports of supernova remnants on her blog Sand & Stars:

 

Sh 2-91

Cygnus Loop & Veil

Vela SNR

 

Of these, Sh 2-91 is the most interesting because the object is so seldom observed . It's the oldest SNR visible in amateur instrument; estimates range from 240,000 to 470,000 years. By compare, the Cygnus Loop is a tyke at 5,000–8,000 years old; the Vela SNR is 11,000–12,300 yro; and Simeis 147 in Taurus is ~40,000 yro.

 

In the professional literature Sh 2-91 is the least studied of all SNR: SIMBAD links only 6 papers, dating from 1976 discovery paper up to a spectral study of all the Sharpless H II emission nebs in 1995. The most informative study is Reich et al 1979. While it is a radio continuum study and depicts emission unseen by us, Section 7 starting on p.275 provides quite a bit of interesting facts on Sh 2-91 and SNRs in general. Frankly, I learned more from Susan's blog than all the SIMBAD papers combined.

 

The Finnish artist/sim producer named J-P Metsavianio has done a superb 3D full-rotation sim of the Cygnus Loop, as though we were at standoff radius watching it all happen. The eggshell-like surface configuration of SNRs really becomes apparent here. You can see a YouTube assemblage of many Metsavianio sims here.

 

=Dana in S Africa


Edited by WeltevredenKaroo, 07 August 2017 - 04:46 PM.


#2 vkhastro1

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Posted 07 August 2017 - 07:01 PM

Susan Young's Cygnus SNR reports are amazing.

Definitely need to download all 3 reports and keep as an deepsky observing reference !!



#3 Kaikul

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Posted 08 August 2017 - 09:34 AM

Very interesting read. I would love to observe these DSO, if only I have darker skies and even lesser night clouds. Thank you for starting this thread.



#4 sgottlieb

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Posted 08 August 2017 - 06:47 PM

Here are few more resources for observing Sh 2-91 -- the other supernova remnant in Cygnus.

 

Bob King (Sky & Tel)

 

Deep Sky Forum (includes observations of the several extremely faint sections with large scopes)

 

Adventures in Deep Space: This page is about 15 years old (my observations are from 2001).  Here's a more recent observation with my 18" Starmaster:

 

Sh 2-91 was immediately picked up in the field of Phi Cygni at 115x and OIII filter as a huge, narrow, faint filament stretching across 13'-14' of field.  It begins close to mag 8.2 HD 185735 and extends to the NE, passing just south of mag 9.6 HD 332384 and continues northeast, brightening somewhat and heads towards a 30" pair of mag 11 stars where it seems to spread out and dim.  Overall, the filament is fairly straight, but gently arcs a bit near the center and at times seemed split into two strands.

 

Although the brightest filament in Sh 2-91 is centered 15' south of mag 4.7 Phi Cygni, there's another section northwest of 9 Cyg (V = 5.4).  At 125x and OIII filter, I was surprised to immediately see a huge filament stretching at least 30' east-west across much of the field (21mm Ethos).  The filament tapered at the east end and fanned out on the west end.  The surface brightness was a bit uneven; brighter along the boundary, particularly noticed on the southwest edge and weaker within the broader fan portion on the west end.  Overall, the visibility was comparable to the better-known filament 15' S of Phi Cyg, although the overall length was longer.



#5 PEterW

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Posted 09 August 2017 - 04:11 PM

Great blog, I have tried for this several times but it yet successfully. Not the only object to evade me! I hope for another attempt in the autumn.

PEterW

#6 Redbetter

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Posted 09 August 2017 - 05:11 PM

If you look down at the end of Bob King's article linked above by Steve, there is a link to the Sharpless Objects Catalog in pdf form which can be downloaded from Reiner Vogel's site.   It is a 126 MB file with finder charts, etc.  This should prove fairly handy for me because I keep coming across Sharpless nebulae visually that are not plotted in Uranometria.   



#7 PEterW

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Posted 12 August 2017 - 04:44 AM

Another poss SNR would be the Eridanus loop (paired to Barnards Loop), another very little mentioned object.
Amazing skies and reports!

PEterW

#8 keesscherer

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Posted 12 August 2017 - 05:35 AM

I made this image of SH2-91 last year:

27665274183_a20146eed5_o.jpgSH2-91, The Swan's second supernova remnant and Campbell's Hydrogen star. DSLR Image by Kees Scherer, on Flickr



#9 SusanY

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Posted 27 August 2017 - 08:24 AM

Hi Dana,
Gosh, thanks for the kind comments about my little Kalahari blog and the SNR posts in particular. SNRs have always fascinated me, but it wasn’t until I arrived under these incredible Kalahari Desert skies - not a drop of light pollution, and amazingly transparent and steady skies - that I really got to see them in jaw-dropping detail. They have certainly been among the highlights of my year’s observing in the Kalahari.

 

Still in SNR mode, last night around about 03h00, I turned my telescope (16” Dobs) on the Large Magellanic Cloud (now that it has finally hoved back into decent observing sight again), and took a squizz at N157B; a faint, broken semicircle of nebulosity on the south western edge of the Tarantula Nebula. My mind boggles when I look at the remains of an exploded star in our own Milky Way Galaxy… but in another galaxy? Mind boggle doesn’t even begin to describe it.


Edited by SusanY, 27 August 2017 - 08:24 AM.


#10 sgottlieb

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Posted 31 August 2017 - 10:45 PM

Squizz?  Had to look that up, Susan!  Here's my observation of this SNR in the LMC from back in 2002.

 

18" (7/8/02 - Magellan Observatory): this fairly small knot of nebulosity is situated just southwest of the main mass of the Tarantula nebula approximately 7' from the center.  About a half-dozen mag 12-14 stars are involved (association LH 99) with a total diameter of 2'.

 

Studies have shown N157B contains a compact x-ray source and a rapidly rotating pulsar, indicating a Crab-like supernova remnant (1998 IAU Circ., 6810, 2).

 

Have you taken a look at LMC N49?  It harbors a powerful quasar and is the brightest SNR in the LMC. There's a great HST Heritage image here.  I was able to take a look with a 24" back in 2008 (from Australia) and found it fascinating...

 

24" (4/11/08 - Magellan Observatory): At 260x unfiltered it appeared as a bright "U" shape just under 1' in diameter with the center of the "U" at the east end (base oriented SW-NE) and open on the west side.  The interior is much dimmer than the rim.  The brightest spot is right at the east end, though the rim is much brighter and better defined along the entire base.  The northern bar of the "U" side is fainter and oriented NW-SE with some haze spreading into the interior.  The southern bar is brighter and narrower.  A UHC filter increased the contrast and there were hints of more complex filamentary structure.  Open cluster S-L 463, which appears as a very small knot attached to a star, is located 2.4' NE.



#11 WyattDavis

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Posted 03 September 2017 - 01:44 PM

Susan,

 

Cool reports. Probably very difficult to see Sh 2-91 visually at the sites I go to, but I will give it a try!

 

PS - are your dogs dob-ermans?



#12 SusanY

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Posted 03 September 2017 - 08:08 PM

Hi Steve,

 

Yes, I took a look at N49 (and N63A) just a couple of days after looking at N157B... and while in their vicinity, I stumbled into the LMX-4 supperbubble... and spent the next two mornings exploring it! What an astonishing region of the LMC.

Here’s my observation of N49 with my 16”:

 

This SNR is the brightest in the LMC... and it is an absolute delight! Especially after the challenge of N63A. Even at 90x it is visible, a tiny, not-quite-round little droplet of bright silky light. The UHC filter improves and brightens the little remnant considerably; better than the OIII filter does.

 

At 150x and with the UHC filter... it’s a splendid sight! A bright little scrap of condensed-looking light that is somewhat dimmer in the centre. Its peculiar shape - almost like a triangle with a rounded apex (the apex to the east) - is apparent and its edges are well defined, except to the north where it appears fuzzy and diffuse. There is the faintest mottling effect to the west.

 

At 225x the SNR is beautiful! It’s a bright and beautiful silky glow, and its central part now looks quite a lot dimmer. I can see what looks like a darker indentation to its west. The northern edge appears even more diffuse and fuzzy, while the rest of its edges are crisp. I can also see a faint star hovering close to its northern edge. What a beauty this little SNR is! Without the filter the tiny little open cluster that lies 2.4' NE is visible - a little droplet of faint fuzzy stellar light.

 

My observation of N63A, embedded in the centre of the fairly bright nebula, NGC 2029, along with half a dozen roughly mag 13 stars, was very challenging. It may appear stunningly bright in the DSS image, but good grief, it is an elusive object. Think searching for a tiny speck of slightly brighter cloud in a slightly bright cloud that has other bright stuff in it! At 225x with the UHC filter I couldn't see it, so I tried 330x and no filter, and there it was with averted vision – an extremely small little dab of light that popped in and out of view.



#13 sgottlieb

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Posted 04 September 2017 - 12:37 AM

You've inspired me to take another look at NGC 2029!

 

Here are my notes from last April in Coonabarabran, Australia using a 14-inch (on my birthday, by the way!).  I mention N63A, but I don't believe I could clearly separate it from the general glow.  Next time I'll try higher power unfiltered.   Are some of the other regions I described part of the LMC X-4 superbubble?

 

14" (4/4/16 - Coonabarabran, 142x): fairly bright, large, over a dozen mag 13 and fainter stars are resolved in a 3.5' region.  A fairly faint, oval emission glow (LMC-N63) is involved with the cluster (S-L 595).  Adding an NPB filter, the nebulosity is bright, large, irregular (roughly round), ~2.5' diameter, with several of the brighter stars still visible.  N63A, embedded near the center of N63, is a well-known bright, compact SNR and one of the first 3 extragalactic SNRs to be discovered (1966).

 

Emission nebula N62A is 14' SSW.  Using an NPB filter, it appeared very bright, very elongated ~E-W, relatively large, ~1.5'x0.4'.  The shape is a bit irregular, but it has a sharply defined northern edge, with the southern edge weaker and more ill-defined.  Visible unfiltered but excellent response to the NPB.  A couple of very faint stars are visible with averted.  BSDL 2348, an LMC cluster perhaps associated with the nebula, is ~2' W and contains a  half-dozen mag 14-15 stars in a 1.5' knot, along with a mag 12.5 star on the west end.

 

Emission nebula N64 is 16' further southeast.  Using an NPB filter, it is a bright, large, irregular nebulous patch, about 3'x2' E-W.  The brightest portion (N64A) is on the west side.  A mag 11 star is ~2' N of the east end.  Another 2' NNW of this star is a detached 40" piece (N64C) that was fairly easy with the filter.  Unfiltered three mag 13 line in a 1.8' string are involved in the central portion, along with a couple of mag 14-15 stars.  Mag 8.8 HD 37853 is 6' NW.



#14 David Knisely

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Posted 04 September 2017 - 02:25 AM

I remember Dragan Niken and I using his 20 inch f/5 and running into Sh2-91 by "accident" while hunting down Minkowski 1-92.  It was not far from Phi Cygni and fairly easy using the OIII filter in that aperture, but it is definitely not plotted on a lot of atlases (I later put it in my copy of MEGASTAR).  Clear skies to you.


Edited by David Knisely, 04 September 2017 - 02:26 AM.


#15 SusanY

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Posted 04 September 2017 - 04:58 AM

Hi Wyatt,
I hope your attempt at Sh 2-91 gives you a glimpse of it; such a remarkable little SNR to see. 

I am wondering what my non-stargazing vet will think when I upgrade little Waldo’s breed from the somewhat ignominious ‘Crossbreed’ to the rather splendid Dob-erman!



#16 SusanY

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Posted 04 September 2017 - 05:12 AM

Steve,

 

Nice birthday pressie to be in Australia looking at the LMC!

 

Yes, the regions you described are indeed part of the LMX-4 superbubble. When I first stumbled into the supperbubble, I was perplexed that my Uranometria didn’t plot a lot of the bright and obvious objects that I was seeing (the stupendous Eighth-Note Nebula, the Quadrant star cloud, the two SNRs, N64 and N62A, among others). So I drew up my own “superbubble map” and explored the region over a couple of early mornings in a row. I posted the map in my latest blog: A Quaver in a Supperbubble in the LMC



#17 WyattDavis

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Posted 04 September 2017 - 05:33 AM

I, too, have a 10" dob (scope, not dog - although I do have two labs...) and am going to the Okie-Tex star party in about two weeks. Will probably get skies of 21.5 MPSAS or better out there, so maybe with that and an O-III filter I will have some luck!



#18 jetstream

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Posted 16 September 2017 - 11:17 AM

From the dark skies up here I have observed SH2-91 for a couple of years now and the 15" makes short work of it when the transparency is on. It is very faint but there is more in the area you can see.



#19 WyattDavis

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Posted 18 September 2017 - 03:00 PM

It's on my list tonight from Okie-Tex...


Edited by WyattDavis, 18 September 2017 - 03:00 PM.


#20 jetstream

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Posted 18 September 2017 - 05:30 PM

It's on my list tonight from Okie-Tex...

Good luck tonight Wyatt, if you see a little chain of stars around Phi Cygni your on the wrong side of it to see the neb. My 10"/Lumicon OIII shows this object under similar skies you describe, eagerly waiting your report!



#21 SusanY

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Posted 19 September 2017 - 08:47 PM

Hi Wyatt,

 

Did you see it? How are your skies? Very keen to read your report! (And what else have you see?)



#22 WyattDavis

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Posted 20 September 2017 - 07:27 AM

Hi Susan, I gave it a go but didn't see it. However, I didn't apply a filter and was on way to NGC7000 on a mission. It was cloudy here last night so I didn't get the chance to try again, but it is supposed to be clear tonight so I will put it #1 on the list. Q:  do you usually use low power + OIII on this object?



#23 SusanY

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Posted 20 September 2017 - 01:17 PM

Hi Wyatt, yes, low magnification and an OIII filter. I hope  you have clear skies tonight and that you get a squizz at this little beauty.



#24 WyattDavis

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Posted 20 September 2017 - 06:40 PM

Roger that. Clear skies - check. Squizzers aligned and cooling...

 

IMG_7164 copy.JPG



#25 WyattDavis

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Posted 21 September 2017 - 10:03 AM

Well, I gave it a squiz last night and no luck in my 8" SCT. Susan, I'm reading your report again today and making more detailed notes. Will give it another go tonight! Stay tuned...




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