Object of the Week, November 6, 2022 – Simeis 147 / Sh2-240, the Spaghetti Nebula

[Howard B]

Taurus and Auriga
Supernova Remnant
RA: 05 39 06
Dec: +27 59 55

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By Georges Attard - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=97460188

For some basic information about this object, see https://en.wikipedia.org/wiki/Simeis_147


Last month while observing under a transparent, high altitude dark sky - with no light pollution - I gave Simeis 7 /Sh2-240 / the Spaghetti Nebula my best shot. I’d never seen it before, although I’ve probably only given it a good effort a handful of times, and never under a really dark sky. I felt optimistic this time because I was using my new 30-inch f/2.7 scope, and given the excellent condition of the sky I felt my time had finally come to see at least the brighter wisps.

Nope!

With and without my filters I was unable to detect the slightest trace of this 3-degree diameter sphere of exploded star stuff and shock wave effects. I spent at least 30 minutes scanning the area of this SNR, which is almost exactly the same size as the Cygnus Loop, and not once did I even suspect any nebulosity.

Like every other time I failed to see it, I realized that the sky wasn’t as transparent as I thought. The sky was very dark – 21.79 SQM - but it was obvious that some of the really faint objects I was revisiting from the night before did not have as much contrast when the SQM readings were about three-tenths brighter. Which shows, once again, that transparency is often more important than a dark sky when trying to see faint objects.

So, my question to those who have seen it – I know Uwe has! – is just how good was the transparency of your sky when you saw the Spaghetti Nebula best, and what filter and magnifications gave the best view? Are the brighter wisps visible in smaller scopes?

And for those, who like me, haven’t yet seen the Spaghetti Nebula - give it a go and let us know.

[oliva]

Hi Howard,

The brightest parts are visible through a 16” telescope. As you mentioned transparency has to be excellent. The only region that I could spot is that one that appears bright and dense and is located around the Star HD 246646 and OIII is the best option. Needless to mention that without filters there is nothing to spot. I could see only a part of the nebula with my 14” Dobson some years ago under the dark sky of La Palma (Canary Islands) and excellent transparency conditions. I figured out some of the brightest parts (http://estelar.de/#Visuelle%20Beobachtung%20von%20Simeis%20147%20mit %2014%20Zoll) and tried them to spot all but only that one around HD 246646 seems to be achievable because of its brightness. I could see around HD 246646 a streak between two stars, that was obviously the brightest part and without any stars in between. The streak (with a brighter knot at its end) could not be hold with adverted vision but popped in and out several times and continuously (also after pausing some minutes).

Spoken about the magnifications you have to use those that gives you a really huge FOV and big exit pupils. I used 40x and 65x with my 14” Dobson for example (with an OIII). Interestingly there are/were some positive observations around the Internet so far, especially with those parts, that are darker than that one around HD 246646.

Oliver

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[lamperti]

Similar to Oliver: with a 22" at 48x with Ultrablock filter back in 11/2015, "Very large. Had to scan around and only caught a few glimpses of nebulosity. Definitely an imaging object." Transparency was 6/10 in my notes. That night I was pursuing other SN remnants in Cepheus, Cassiopeia, Perseus & Taurus.
Al

[Clear Skies]

This fascinating (but faint!) SNR is amongst the Simeis objects for which I have recently completed observing guides. I am hopeful to publish guides for all Simeis objects - and much more (https://clearskies.eu/csog/futurecsog/) - a year from now.

Simeis 147 is the designation for the supernova remnant as a whole. Filtering information from the treasure trove of information that is the Gaze-Shajn papers, I have uncovered that Simeis 147 itself involves three more Simeis objects: 149, 151 & 155. They're the three brightest "intersections" of the spaghetti-like tendrils of this SNR.

I have labeled them in the observing guide for this week's OOTW: click here (https://clearskies.eu/csog/downloads/dsfootw2022#45) to download. Also included are the Gaze-Shajn catalog notes for Simeis 147, 149, 151 & 155.

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The image on the second page of the guide is from renowned Dutch astrophotographer Maurice Toet (https://www.mauricetoet.nl), used with permission. It shows a lot more detail than the DSS image does.

I have yet to log an observation for this (these) object(s). But I will surely give the brighter sections a try, especially now that they have regained their historically correct designations!

[Howard B]

Thanks Victor, I'll use your observing guide the next time I give the Spaghetti Nebula a shot!

[akarsh]

I have known this object as "Simeis 147" rather than as "Simeis 7" -- perhaps a typo? Scott Harrington and Victor van Wulfen have been poring through the Shajn and Gaze papers that I somehow managed to find, so they would know more about the Simeis designations.

Many many years ago, I found these articles on Adventures in Deep Space which tackle the formidable challenge that the Spaghetti Nebula poses to visual observation:
https://www.astronomy-mall.com/Adventures.In.Deep.Space/simeis.htm
https://www.astronomy-mall.com/Adventures.In.Deep.Space/s147.htm

Searching for finder charts, the following pops up:
http://macalchemist.net/yabb/YaBB.pl?num=1225028981
The forum post calls the notable clump of nebulosity the "Spider", which is referenced to as "Region D" in Rich Jakiel's adventures post.

I figured I should try the "Spider" region first, since it is ostensibly the brightest part, and after many attempts finally succeeded in seeing something in October 2020. Since I don't have my observing logs with me presently, I'm sharing my observation as described in an e-mail on my local forum TAC:

"After many failed attempts, I finally saw this object briefly amidst the brightening dawn zodiacal night during my last new moon run. I focused on the fragment "D" that another source monikers the "Spider". The brightest part of this, in my observation, seems to be a small condensed patch seen at 05:42:45 +28:22:00, just south of a bright-ish star. I did see some filaments flowing through my eyepiece field, but it was bedtime, so I didn't study them."

This observation was made from Modoc National Forest near Likely, CA, USA -- a Bortle 1 sky site. My faint memory wants me to believe the transparency was also excellent, although seeing was modest.

Looks like I have to give it another go.

[Uwe Glahn]

First I want to highlight Oliver's article above. Best reading I know. I recommend to use a translator to understand what he saw and write about this SNR.

Second, and directly to the question of Howard after the needed transparency. I had best conditions during both times I gave the object a detailed go. But I'm sure transparency is not the most important thing, because I also failed to see this object by having perfect skies.

The key is to know exactly were to look at and what to look for. Scanning the object is definitely to little to have success. You need at least an accurate [OIII] image, no Halpha, no RGB, no DSS, simply a pure [OIII] image. Oliver already linked two sources here (https://i.imgur.com/pwUIzuM.jpg) and here (http://www.astrosurf.com/zoll/images/SH2_240_HvsO.jpg). The use a maximum EP (with 25"+ class around 100x) and [OIII] filter is a must. Good seeing conditions are not necessary.

After my experience you should start at the middle section near HD 246646. First detail to look at is a slightly bend 8' long filament. You can see that in my sketch and in the [OIII] image. The level of difficulty is comparable with the filaments of Sh 2-91, not harder. The difficulty here is the rich star field. But again, equipped with a accurate map the filament should be no problem with a 25"+ telescope. Beside the filament, some more brightening are visible in the near.
Scanning the whole complex I had success with a much more difficult part at the SE edge of the SNR. I could detect the edges of the brightening between the 8mag stars GSC1 1869-00102 and GSC1 1870-00033.

I knew about observations with much smaller apertures or binoculars. I also tried it several times but never had any glimpse. I also tried Hß filters but again had no success.

sketch: 27", 113x, [OIII], NELM 7m0+, Seeing IV
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home (http://www.deepsky-visuell.de/Zeichnungen/Sh2-240.htm)

[j.gardavsky]

Hello fiends of the supernova remnants,

and thanks to Oliva and Uwe for the sketches!

According to the deep astrohotos my impression is, that the Simeis 147 is a bundle of very thin filaments, requiring large apertures to see at least some of these filaments.

On the side of the small apertures and big binoculars, the trick is to observe at the lowest magnifications to visually turn this SNR into a sort of donut of unresolved filaments.

During 2020/2021, I have had 4 successful observatins through the 15x85 (BA 8 Kunming) binoculars. The best view has been through the OIII filters, some condensations on the "donut" became visible through the H-Beta and blue(RGB)CCD filters.

Rating the difficulty to see at least something on the Sim 147,
I would say that the SNR G179.0+2.6, south of M37 in Auriga, has been more difficult for my eyes.
Also in Auriga, another SNR, the Sh2-224 (G166.0+4.3) has been definitely easier to see than the Sim 147.

A good reference object for checking the transparency of skies in this area is the 'forgotten' Gaze Shajn [GS-55]75, a N-S streak (90 arcmin long) between M36 and M37.

Clear skies,
Jiri