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(IAAC) Sh2 242



> 
> > -----Original Message-----
> > From: Murray Cragin [mailto:murastro@fwb.gulf.net]
> > Sent: Tuesday, January 26, 1999 10:34 PM
> > To: artrussell@mindspring.com; driddle941@aol.com
> > Subject: Sh2-242 et al.
> >
> >
> > Regards Sharpless 242, et al. As usual, there seems to be little agreem=
> ent
> > between the various catalogs and associated computer mapping
> > programs which
> > display them. Here is the data found so far according to the
> > mapping software:
...
[stuff deleted]
...
> > Unfortunately, I don=92t have a hard copy of either the Sharpless or th=
> e DG
> > (Dorschner and Gurtler) catalogs to see if they offer any
> > clarity. Bottom line
> > is, the AGC does show a large, round nebulosity. But how Lynds
> > could see two
> > distinct objects, how D and G could see two distinct objects,
> > while Sharpless
> > saw one wee little object, truly escapes me. But as I pointed out
> > above, this
> > is part of the joy of doing catalog research. And don=92t place any
> > big bets on
> > SIMBAD getting it right either, I=92ve found some really bad errors in =
> this
> > Mother of all online catalog sites!
> >
> > Bottom line is, there=92s definitely a BN there, but tagging it
> > with names can be
> > very dangerous. One nebulous patch, six distinct names (LBN
> > 826/827, DG 83/84,
> > S 242, MRSL 68); and, diameters that run from one arcminute up to 10
> > arcminutes! We can put a man on the Moon, but we can=92t give one
> > lousy name to
> > one lousy piece of gas and agree on it=92s size!
> >
> > Enjoy=85
> >
> > Murray Cragin
Murray, Lew, Dave, and others -
I've never observed this apparent H II region, but it sounded
interesting enough that I decided to try to look into the object
identifications somewhat.  I think I've cleared up most of the problems
that Murray notes with many different sources.  Let's take the
designations in order here.  (Although I don't have the MRSL reference
so am not going to consider it at the moment.)
Sharpless 2
===========
Murray mentions that he doesn't have a copy of the Sharpless catalogue. 
It was published in 1959 as follows:
Sharpless, Stewart [1959].  "A Catalogue of H II Regions," _The
Astrophysical Journal Supplement Series_, v. IV, pp. 257-280, December.
The preferred designation for names in this catalogue is "Sh2" or
"Sharpless 2" - the "2" is important because this is the _second_ such
catalogue by Sharpless. The "Sh" is important to distinguish this from
the similar "Simeis" catalogue of H II regions, often (incorrectly
designated) "S".
Sh2 242 is listed on p. 262, with the following data:
Position (1900.0): 05 45.6 +26 59
Diameter: 7'
Form: 1 [circular]
Structure: 2 [between amorphous and filamentary]
Brightness: 2 [between faintest and brightest]
Stars: [none]
There are no notes or listed stars.
The given position updates to (2000.0) 5 51.9 +27 01, and sure enough
the DSS shows a nice bright nebula (presumably an H II region) right on
that position.
By the way, the current ADC version of this catalogue
(ftp://adc.gsfc.nasa.gov/pub/adc/archives/catalogs/7/7020/catalog.dat.gz)
does give the correct size of 7' (line 242, column 52).
DG
==
The reference here is:
Dorschner, Von J. and Jena G\"{u}rtler [1963].  "Untersuchungen \"{u}ber
Reflexionsnebel am Palomar Sky Survey.  I. Verzeichnis von
Reflexionsnebeln," _Astronomishe Nachrichten_, v. 287, pp. 257-260.
Object 84 there is listed at (1950.0) 5 48.8 +27 01, with a blue plate
size of 3' x 3', and a red plate size of 8' x 8'.  The position updates
to (2000.0) 5 51.9 +27 02.  Obviously by position and size, this is the
same object as Sh2 242.
Lynds
=====
The Lynds designation comes from:
Lynds, Beverly T. [1965].  "Catalogue of Bright Nebulae," _The
Astrophysical Journal Supplement Series_, v. XII, pp. 163-186, August.
The first thing to realize is that Lynds _did not_ number the objects,
but instead gave them by Galactic coordinates.  The "LBN" numbers were
assigned by others later, following the sequence she used (not unlike
Flamsteed numbers - yes, which were never used or given by Flamsteed!).
Secondly, Lynds lists two nebula at this location - 1 minute of RA
apart.  Her "LBN 826" (actually 182.30+0.07) she says is "S 242", while
here "LBN 826" (actually 182.41+0.27) she says is "DG 84".  I've already
shown that Sh2 242 and DG 84 are one and the same object, so obviously
she simply mistakenly listed them separately.  She also gives the wrong
size of "10' x 10" for "DG 84", since as shown above the DG catalogue
gives this as either 3' x 3' or 8' x 8'. 
Conclusion
==========
This all adds up to the following:
Name: Sh2 242
Aliases: DG 84, LBN 826, LBN 827, LBN 182.30+0.07, LBN 182.41+0.27
Position (2000.0): 05 51.9 +27 01 (Sharpless's)
Diameter: 8' (measured from DSS)
If I'm missing something, please let me know of any comments or
questions.  Also please send a copy of your message to me directly, as
I'm getting only the digest version of the netastrocatalog-announce
messages.
Regards,
- Brent
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