| Abell 31, aka The PN was discovered in 1955 by George Abell on the POSS plates. The optical diameter is 970", which is nearly the diameter of the Helix Nebula. It is apparently an ancient planetary that is interacting with the surrounding interstellar medium. As the nebula is so big, its surface brightness is very low, with surface magnitudes of 27 arc-sec-1. The nebula is brighter in [OIII] signal than [HII].The OIII portion sits close to the progenitor star. The southern portion is bounded by a wide "bow shock" where the nebular material is apparently interacting with the surrounding medium. |
Abell 31, ( = PK 219.1+31.2 / SH2-290 Abell31 est une très grande nébuleuse planétaire localisée dans le Cancer, découverte par G. Abell. La taille très importante de la nébuleuse (similaire à Helix) lui confère une luminosité surfacique très faible, typique des NP anciennes se diluant dans l'espace, la rendant difficile à photographier ou à observer. Le signal OIII est le plus fort et plus localisé dans la partie centrale de la nébuleuse. Magnitude: 12.2 Luminosité de surface: 27 arc-sec-1 Dimension: 970" (~16x16') |
 Composite "HOO" color image R=H-alpha (4h45) G=OIII (3h45) B=OIII Takahashi FSQ106ED refractor CCD camera Atik 4000 (Kodak KAI-4021M) @-20°C Astrodon 6nm bandwidth filters |
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 Comparison with M27: size and brightness (log scale). 
Relative response for the two considered emission lines.
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 color variations |
Other images: http://dg-imaging.astrodon.com/gallery/display.cfm?imgID=236 http://sharplesscatalog.com/sharpless/SH2-290.aspx http://www.capella-observatory.com/ImageHTMLs/PNs/Abell31.htm http://observing.skyhound.com/archives/feb/PNG_219.1+31.2.html |
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