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(IAAC) FW: Sh2-242 et al.



Lew, et al.,

Attached is Murray Cragin's response to my query about this object.

Cheers!

Art Russell

Atlanta, Georgia

mailto:artrussell@mindspring.com
http://Education.gsu.edu/spehar/

Member National Deep Sky Observers Society (NDSOS), Webb Society, and
Association of Lunar and Planetary Observers (ALPO)

"Sight is a faculty; seeing, an art" - George Perkins Marsh

> -----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 agreement
> between the various catalogs and associated computer mapping
> programs which
> display them. Here is the data found so far according to the
> mapping software:
>
> Megastar: SH2-242 = LBN 826 = 05 51 48.0 +27 01 20 (2000.0),
> diameter 7.1í X
> 6.5í
>
> HyperSky: This program places a glyph on-screen for all catalogs
> selected from
> itís rather huge database. In this case, the Sharpless Catalog of
> HII Regions;
> 1959, which contains 313 emission nebulae, and which has been
> taken from the
> ADC catalog obtained from the University of Maryland in 1979.
> Also displayed is
> the Lyndís Bright Nebulae catalog. Here is their data for all the
> players, as
> displayed by HyperSky, with data from the catalogs (equinox 2000.0):
>
> LBN 827 = 05 52 07.0 +27 00 0.40, diameter 10í X 10í, = DG 84
> Brightness = 3 (med+), color = 3 (red)
>
> Sharpless 242 = 05 51 51.5 +27 00 37, diameter 1í (thatís one arcminute!),
> circular, type Ne, structure = amorphous+filimentary, brightness
> = intermediate
>
> LBN 826 = Sh2-242 = 05 51 07.0 +27 00 45, diameter 7í X 7í
> Brightness 3 (med+), color 3 (red)
>
> As you can see from the catalog data, the Sharpless catalog gives
> S 242 a very
> small diameter of only one arcminute, and actually places it within the
> boundaries of LBN 827, not LBN 826. And as noted in the message from Art
> Russell, no mention is made of LBN 827 in Megastar. Also note
> that in HyperSky,
> the LBN entry for LBN 826 says itís S 242. Welcome to the joys of
> cataloging!
>
> The AGC  states that the image it shows is LBN826/827 = DG 83/84
> = S 242 = MRSL
> 68.
>
> Looking at a hard copy of the MRSL (ďA Comparison Catalogue of
> H-II RegionsĒ by
> Pavla Marsalkova, shows that itís source for MRSL 68 is the
> Sharpless (1959)
> catalog; but, the MRSL shows a diameter for MRSL 68 of 7
> arcminutes! This is in
> stark contrast with the ADC machine readable version of the
> Sharpless which
> give S 242 a diameter of one arcminute! Go figure?
>
> Unfortunately, I donít have a hard copy of either the Sharpless or the 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 donít place any
> big bets on
> SIMBAD getting it right either, Iíve found some really bad errors in this
> Mother of all online catalog sites!
>
> Bottom line is, thereís 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 canít give one
> lousy name to
> one lousy piece of gas and agree on itís size!
>
> EnjoyÖ
>
> Murray Cragin
>
>
>
>

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