Object of the Week, January 30, 2023 – Simeis 22 / Sh2-188

[Howard B]

Cassiopeia
Planetary Nebula
RA: 01 30 30
Dec: +58 23 30

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DSS image of Simeis 22 / Sh2-188

I was inspired after reading Scott Harrington’s article in the December 2022 issue of Sky & Telescope. He wrote about planetary nebulae in Cassiopeia, many of which I wasn’t familiar with, so I put my copy of the magazine in my observing bag so I’d be ready for the next clear night. Unfortunately, I’ve only had one night since then with a good enough sky to give some of these nebulae a shot. Happily, Simeis 22 was surprisingly easy to see from my semi-dark backyard.

To find out more about this PN, I refer you to either Scott’s excellent article or this page (https://www.deepskycorner.ch/obj/sim22.en.php). I won’t rehash all that here, and will concentrate on sharing my observing experience of this intriguing object.

Located about 2 degrees south of magnitude 2.7 Delta Cass (Ruchbah) and about 1.5 degrees east of the popular open cluster NGC 457, Simeis 22 is relatively easy to find in even a moderately light polluted sky. Easy enough that I found it on my first try, which isn’t always the case.

It was immediately visible in a low power eyepiece + OIII filter, which framed it quite nicely. My notes:

“This is a pleasant surprise – I can see an arc of nebulosity. Its edges are indefinite and I can’t tell if I’m really seeing an arc or a straight segment of the nebulosity. A faint stream of stars intersects its western end, giving the impression of the nebula curving along with it. 113x, OIII filter, 20.24 SQM (30-inch f/2.7)”

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North is to the upper right in my sketch, and you can match the small curl of stars near the western end of the nebulous arc to the DSS image.

Simeis 22 was invisible without the OIII filter, but I have the feeling it could be seen in a darker sky, and that the strongly curving arc would be more pronounced with an OIII then too. Time will tell as I definitely plan to come back to this wonderful object.

In the meantime - well, you know!

[Steve Gottlieb]

I made a couple of observations of Simeis 22 back in the '90's with my 17.5-inch. This unusual planetary was *really* little known at the time, despite the fact it's situated very close to the fan-favorite open cluster NGC 457 (1.5° to its east).

12/16/95: Simeis 22 was picked up at 100x without filter as a very low surface brightness haze, elongated E-W and involved with five mag 13-14 stars. The planetary was difficult to identify with certainty as it's located in a rich Milky Way field, along with other similar appearing patches of unresolved stars. But it was confirmed using an OIII filter, which gave a moderate contrast enhancement and brought out some structure. The 4' strip tapers down at the west end and broadens on the east end, where the nebulosity then abruptly curves towards the north.

Steve

[Clear Skies]

In September, I was about to log my first observation for this object. Centered it and picked it up using a UHC filter with my 14" SCT and a 17mm eyepiece. As as was about to log my description for this nebulous arc, the clouds rolled in, ending the session...

So unfortunately that's all I can say about it, for now: well visible in a 14".

Here's the guide (https://clearskies.eu/csog/downloads/dsfootw2023#5) for this planetary.

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[Ciel Extreme]

I have an observation from September 15, 2014 from my backyard, using an 18" f/4.5 reflector at 207x, no filter used. Seeing was 6/10 and the NELM was 6.0:

“This nebula is extremely faint and very difficult but the sketch agrees well with the DSS image. Appears as a very hazy and indistinct, crescent-shaped glow involving five faint field stars near the western terminus of the nebula. The nebula curves from the ENE to the west; about 7x1 arc minutes in size.”

[ScottH]

Well, Howard, it feels good to know that someone found my article useful! Truthfully, of all the PNe I covered, Simeis 22 took the most research time because of its complex backstory. Glad I was able to save you some work.

Mark Bratton's sighting with an 18-inch is the smallest aperture I've now heard of it being seen in without a filter. Good job!

Scott H.

[akarsh]

I'm pretty bad at the "keep up with S&T game", so I'm glad you highlighted Scott's article, which looks like it's a "must read" :-).

Not sure where I found out about this object from, but it's one of the few objects I logged on Dec 12th 2015 from the 3 Rivers Foundation's Commanche Spring Astronomy Campus near Crowell, TX.

I wrote of the conditions "Sky transparency is okay. Seeing poor. Very dark! Zodiacal band hints. Thick winter Milky Way"

Of the object itself, I wrote "Best views in 26mm University Optics ortho and 20mm Pentax XW with OIII. Can sense and hold the nebula well with averted, somewhat mottled and thick, but no filaments visible." and made the following rough sketch:
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[Howard B]

I think Steve gets the prize for the smallest aperture to see Simeis 22 without a filter so far, but by just a half inch!

[akarsh]

My general experience with low—surface brightness objects like this is that they are more sensitive to sky quality than to aperture. I would not be surprised if someone reports seeing it in a high-quality 6" under excellent conditions :-).

[akarsh]

In Scott's article, he says that Simeis 22 is called the "Dolphin" by astrophotographers. Frustratingly, this moniker also seems to apply to Sh2-308, the bubble blown by Wolf-Rayet star EZ CMa: Searching for "Dolphin Nebula" on Google images results in pictures of both, although thankfully, Sh2-308 is sometimes disambiguated as the "Dolphin Head" nebula. I shall add this to my list of frustrating astronomical names, with "Pinwheel Galaxy" topping the list.

[j.gardavsky]

My general experience with low—surface brightness objects like this is that they are more sensitive to sky quality than to aperture. I would not be surprised if someone reports seeing it in a high-quality 6" under excellent conditions :-).

Hello all,
so far I have not been successful with this PN through my 6" F/5 achro, but I don't easily give up.

Clear skies,
Jiri

[Uwe Glahn]

I logged a nearly 20 years old observation under very good transparency with my old 16-inch.

I wrote: difficult object despite 7mag limiting magnitude sky and high position in the sky, not visible without filter, best view with 51x with [OIII], large slightly bend object with thicker bulge and indicated fibrous structure, faint stars shines through the filter

sktech: 16", 51x, [OIII], NELM 7m0+
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home (http://www.deepsky-visuell.de/Zeichnungen/Simeiz22.htm)

[ScottH]

Oh, thanks for pointing that out, Howard. I overlooked that part in Steve's notes. Now I need to try for it in my 16-inch since I didn't even own it when I made the observations for that article.


My general experience with low—surface brightness objects like this is that they are more sensitive to sky quality than to aperture. I would not be surprised if someone reports seeing it in a high-quality 6" under excellent conditions :-).

Well, I would! I've gone a few rounds with this PN and it's fainter than it looks on images (though I have found it visible in 5-inch and 6-inch telescopes with the appropriate filter, Jiri). As to its nickname, Akarsh, one thing you don't know about me is that I'm biased when it comes to such things. I only repeat a nickname if it makes a lot of sense and in the case of Simeis 22, it really does look like a dolphin to me in some images! So of the two, S 22 gets my vote as the "Dolphin".

Scott H.

[akarsh]

I only repeat a nickname if it makes a lot of sense and in the case of Simeis 22, it really does look like a dolphin to me in some images! So of the two, S 22 gets my vote as the "Dolphin".

Scott H.

Yep, definitely way more appropriate to call Simeis 22 the “Dolphin Nebula”, and Sh 2-308 the “Dolphin Head Nebula”.

[j.gardavsky]

Hello Scott,

good to know, that you have seen it through the 5" and 6" telescopes.
This is encouraging,
Jiri

[Robin]

Beautiful planetary nebula! I observed it last weekend with my 20" Dobsonian at 128x magnification with O-III filter (although I was able to glimpse it without filter). Crescent shape, about one quarter of an annulus.
Please find attached my sketch.

Clear skies,

Robin