Object of the Week, February 24, 2019 - Messier 46, NGC 2438 and the Calabash Nebula

[Uwe Glahn]

- OC: Messier 46
- PN: NGC 2438
- PPN: OH 231.8+4.2 ("Calabash Nebula", Rotten Egg Nebula")

Puppis
~RA: 07 42
~DEC: -14 48

"Deep, deeper, tough nut" could be the motto for the actual OOTW. Within a frame of around 20' we find three totally different objects for all kinds of telescopes and likes.

Lets start with the brightest one - Messier 46. Discovered by Messier itself in 1771 it is just visible with the naked eye under dark skies. With binoculars and small telescopes it forms a very nice trio with the two other OC Messier 47 and NGC 2423. The cluster itself counts around 500 stars and is a beauty in nearly all kinds of telescopes. The distance is around 4900ly.

Around 100 years later William Herschel discovered the PN NGC 2438 within the stars of Messier 46 in 1786. Personally I already pick out the object with a 4-inch bino without any problems. Most people name the bright 13mag star near the middle as the central star. But this false CS (which is a tight double with a 16mag companion) is shifted to the NW. The real CS stands 7" SE. With its 17.7mag the star is a hard target (the nut comes later) for bigger telescopes. Beyond the bright PN shell there is an extended double halo. I could not catch it yet with the 27-inch. Most sources speaks about a distance of around 2900ly. So the PN seems to lie in front of the OC.

The "tough nut", the Calabash nebula was already discussed here at February 23rd, 2012 (http://www.deepskyforum.com/showthread.php?75-Calabash-nebula-observation). It lies only 6.5' E of NGC 2438 so it is worth a comment. Physically the nebula belongs to the Protoplanetary nebula (PPN). It was first photographed in 1977 [1977ApJ...211..178C]. The name "Calabash Nebula" was first proposed in 1989 [1989A&A...211..409I]. The 27-inch brings out the first hints of the brightest knot. But even a 36-inch didn't show the longish and/or the bubble structure.

Picture (downsized): Adam Block/Mount Lemmon SkyCenter/University of Arizona
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Original: http://www.caelumobservatory.com/gallery/n2438.shtml

sketch Messier 46: 20x125, NELM 6m0+, field 3°
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sketch NGC 2438: 16", 360x, NELM 6m5+
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"Give it a go and let us know"

[Raul Leon]

Hi, this is my observational sketch of ngc 2438 from 11/9/2007 with my 14.5 inch Dob f/4.3 using a 10mm Radian at 158x , no filter was used3447 The Calabash nebula is too faint for my aperture.

[Howard B]

Excellent choices for the OOTW Uwe! I only have a sketch of NGC 2438 from ten years ago with my 28-inch:

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" A perfect ring of smoke, grey without a hint of color. A conspicuous star is inside the ring but is slightly off-center. The PN is slightly thinner / fainter on the side closest to the inner star but is still an obviously complete ring. 408x"

I didn't realize how close by the Calabash Nebula is to 2438, if conditions allow I'll give that a go before winter is over.

[FaintFuzzies]

Like Howard, I had no idea that the Calabash Nebula was that close to the PN in M-46. Pretty cool. Probably won't catch much in my 22", but I'll give it a shot.

[KidOrion]

And don't forget M1-18, also in the same field!

[Bertrand Laville]

Hi All,

Apologies for posting Andromeda's parachute and this post in a couple of days, which can be disturbing when looking for one of these both.

Here is my sketch of the field of M 46, with my 25" . PN and PPN have been observed at 520x, in average conditions: SQML 21.4, S 2.0", NELM +/- 7.0v at zenith.
NGC 2438: I saw four stars on and inside the PN.
Calabash has been seen with very difficulties, and only the "stem" of the PPN, not the "belly".

Here are my reports:
for NGC 2438: http://www.deepsky-drawings.com/ngc-2438-t635/dsdlang/fr
for the Calabash: http://www.deepsky-drawings.com/oh-231-8-4-2/dsdlang/fr

Clear skies
Bertrand
http://www.deepsky-drawings.com

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