Sharpless 91 and Friends: The complete ring of the G65.3+5.7 SNR

[reiner]

This SNR is just north of Albireo in Cygnus and comprises Sharpless 91, 94 and parts of 96, but also other parts that bear no further designations. Its size and appearance is similar to that of the Veil, but it is farther away (2500 instead of 1500 LYs), considerably older (estimated 30000 instead of 7500 years) and hence much dimmer.

This SNR was discovered as a SNR by Kirshner, Gull, and Parker in the 70ies. The first "good" OIII image is by Fotis Mavromatakis from Shinakas Observatory in Crete from 2002.

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image: http://arxiv.org/abs/astro-ph/0204079v1

Here is a finder chart as an overlay with the OIII image with the main filaments being numbered

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larger chart: http://www.reinervogel.net/artikel/Images/SH91_finderbig.jpg


The Sharpless 91 part constitutes, of course, the brightest part of the SNR. This part comprises, however, much more than only the tip of the main filament south of Phy Cygni. Surprisingly, the filaments in the unnamed NE segment are not considerably fainter and appeared to me easier than that of Sharpless 94 and of course that of Sharpless 96.

Here are my observing notes of the single filaments (still to be continued):

Sharpless 91 filaments

The brightest part of the SNR is filament 01, which is directly SE of Phi Cygni and which appears as a very faint narrow segment. Coming from NE, it is passing through mag 8.2 star HD185735 about 15' south of Phi Cygni. The filament extends beyond this star, becoming fainter and more diffuse. After having passed behind 9 Cygni, it can be picked up again as a better defined filament 02, and even the bifurcation towards 2 Cygni to the west can be perceived. Parallel and NW of filament 01 is extremely faint filament 03, which I have not observed yet. Filament 04 is even a bit further NW and appears fainter and narrower than filament 01. The observation can be verified by its precise location relative to a mag 7 and two mag 8 stars aligned to it. In the very west is filament 05, an extension of filament 02, which I have not observed yet.



Sharpless 94 filaments

The filaments of Sharpless 94 are considerably fainter than those of Sharpless 91. After many unsuccessful attempts, I was able to observe the southern end of filament 11 as an extremely faint N/S oriented elongated glow. Towards north, the filament merges with the background and I could not trace it up to the two conspicuous mag 10 stars.

The southern E/W oriented filament 12 could not be observed up to now.



Sharpless 96 filaments

Sharpless 96 comprises besides the long SNR filament also HII regions, which are possibly not associated directly with the SNR. The catalog position of Sh2-96 is therefore not coinciding precisely with the position of the long SNR filament.

In this area, filament 21 was several times suspected as an extremely faint and narrow filament.



NE filaments

This series of filaments does not bear any catalog designation. Of these filaments, filament 33 appeared as the most distinct. It trails between the two mag 7 and mag 8 stars HD185602 and 185660 and can best be viewed about 15' west of this pair as an extremely faint structured glow slightly above the background. Further towards E, filament 32 becomes somewhat fainter and was visible as an extremely faint patch trailing north of another fainter pair of stars. Filament 31, which appears relatively bright on the OIII images, was similarly bright. Its very narrow angled southern end was about similarly difficult as the broader part of it that trails towards NW. At the other end of this part of the SNR is filament 34, of which the brightest part appeared as an extremely faint elongated patch.



Central filament

Filament 41 is in the central part of the SNR and is an extension of filament 04, turning towards west. Not yet observed.


More information, links to images and to papers is on my website

http://www.reinervogel.net/artikel/Sh91_SNR_e.html

[Steve Gottlieb]

Fantastic post, Reiner! Thanks for revealing the entire G65.3+5.7 ring. I enjoy showing off Sh 2-91 (portion near Phi Cyg) at star parties as the "next best SN remnant in Cygnus".

[reiner]

Thanks, Steve!

Last weekend I visited this SNR again under alpine skies.

Filament 02, the part of Sh91 close to 9 Cygni, appears to me even easier than the "classical" filament 01 next to phi Cygni. I also observed all filaments of the NE loop and the brightest filament of Sh94. I still have some problems with the Sh96 filaments 21 and 22. Though there always appears to be something, I am not fully convinced as this is a very dense starfield and you see "something" with the OIII filter any place there, if you just stare long enough ;-)

[mkronber]

Hi Reiner et al,

here's some of my observations of the SNR ring, which has been amongst my summer favourites for several years now. Instrument was an Obsession 15" UC, magnification + filter = 160x + [OIII], unless otherwise noted. Location: Tiefenbachferner, Oetztal, Austria (altitude 2900m). The part numbers refer to Reiner's superb finder chart (see above) that I used in the observations together with Stephane Zoll's [OIII] images of the brightest filaments.

Part 01:
despite the rich stellar field, the filament is easily detectable with averted vision as a diffuse arc south of phi Cygni. Especially the easternmost edge of the filament is easy to see; in western direction, the filament gets gradually fainter, however can be followed for several tens of arcminutes until NW of the star SAO 97498.

Part 02:
also easily to detect, especially the westernmost end of the southern filament is conspicuous. The bifurcation of the filaments NW of 9 Cygni and the northern filament were also not difficult to detect, whereas the eastern bifurcation was not doubtlessly detectable.

Part 04:
fainter than parts 01 and 02, but nonetheless surprisingly easy to see as a stretched, slightly curved band immediately W of three brighter stars.

Part 11 = Sh2-94:
especially the southern part of the N-S streched filament was surprisingly easy to detect as a N-S oriented band with indications of structure. Definitely visible also with lower aperture and/or under less good conditions.

Sh2-96:
Definitely the faintest observed part of the SNR. Part 21 was very faintly, but definitely seen as a E-W oriented brightening N of two medium bright stars. Part 23 and some more filaments of Part 21 were also faintly indicated, but less well defined than the filament mentioned before. Part 22 totally visible.

Part 31:
similarly bright/faint as part 04, appeared as a curved band of faint nebulosity. Particularly interesting is SE-tip of the filament: Here, there is a short but comparably bright, N-S oriented filament to find. The filament was not very conspicuous at 160x + [OIII] (also, some field stars are disturbing the view), but appeared distinctly as a short, narrow, elongated brightening at 228x + UHC filter.

Parts 32 + 33:
detectable as a very faint, broad band of nebulosity. Difficult to observe unambiguously without detailed chart due to the rich MW background in this area that triggers a lot of false detections.

CS,
Matthias