by neufer » Thu Jan 22, 2009 3:05 pm
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<<
Pyxis is a small and faint constellation in the southern sky. Its name is Latin for a mariner's compass (it should not be confused with Circinus, which represents a draftsman's compass). Pyxis is completely visible in latitudes south of 53 degrees north from January through March. Pyxis (Latin: box) was introduced by Nicolas Louis de Lacaille in the eighteenth century; he called it Pyxis Nautica, but the name was shortened. The constellation is located close to those forming the old constellation of Argo Navis (the ship Argo), and in the 19th century astronomer John Herschel suggested renaming Pyxis to 'Malus, the mast', but the suggestion was not followed.>>
http://www.astrosurf.com/antilhue/ngc_2818_in_pyxis.htm
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_The unique planetary nebula NGC 2818_ by Dufour, R. J.
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 287, Dec. 1, 1984, p. 341-352.
<<The planetary nebula NGC 2818, or PK 261 + 8 deg 1, is of special interest due to its apparent association with a Population I open cluster (of the same designation). The results of new observations of the nebula are presented, including interference-filter imagery, photoelectric photometry, and ground-based and IUE spectroscopy. Analysis of its composition based on new IUE and ground-based spectroscopy and model calculations of the very similar planetary nebula NGC 2440 suggests that NGC 2818 is a prototype of the He-rich and N-rich Type I group.
NGC 2440 :
http://antwrp.gsfc.nasa.gov/apod/ap070215.html
http://antwrp.gsfc.nasa.gov/apod/ap060507.html
Compared to the composition of H II regions in the solar neighborhood, He is 60 percent overabundant, C is 0.3 dex lower, N is 1.0 dex higher, and O, Ne, Si, Cl, and Ar are essentially at comparable values. Analysis of kinematical and morphological data suggests that the nebula is probably associated with the star cluster (revised distance = 3.5 kpc). If so, then it is of exceptional size (radius approximately 1.1 pc), mass (greater than or equal to 0.6 solar mass), expansion velocity (52 + or - 3 km/s), and age (possibly as old as 22,000 yr). Some implications of the results regarding the masses of planetary-nebula progenitors, the nucleosynthesis processes in stars of intermediate mass, and the formation of planetary nebulae are also discussed.>>
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http://www.skyhound.com/sh/archive/mar/NGC_2818.html
<<Where the heck have I been? That's what I found myself thinking as I looked at this wonderful planetary nebula embedded in an open cluster. These two objects both share an NGC number and some references use the designation 2818A to describe one or the other of the two. Planetary nebulae in open clusters make for a rare visual treat and the planetary that appears to lie in M46 is one of my all-time favorite objects.
M46:
http://antwrp.gsfc.nasa.gov/apod/ap060910.html
http://antwrp.gsfc.nasa.gov/apod/ap990305.html
The planetary nebula NGC 2818 is relatively large and bright with interesting structure. This planetary is similar in size and brightness to the much better known "Bug" (NGC 6302) in Scorpius.
NGC 6302:
http://apod.nasa.gov/apod/ap070429.html
http://antwrp.gsfc.nasa.gov/apod/ap980602.html
It's relatively high surface brightness takes magnification well. Look for the appearance of two separate, parallel, lobes that arc toward one another, nearly touching at the ends. Also look for a fainter outer envelope, particularly off each end, using averted vision. I didn't detect any color, but Steve Coe notes that "A few dark lanes are seen in the planetary at 165X, it is light green at all powers." Although NGC 2818 has a lower surface brightness than NGC 2438 (the PN in M46) it does compare favorably and its intriguing structure will surely bring me back again and again.
The NGC 2818 cluster is fairly faint, mostly made up of 11th to 14th magnitude stars. It is scattered and irregular and does not immediately jump out at you as a cluster of stars. It doesn't begin to compare to M46. Regardless, the many stars do make a nice backdrop for the planetary. Interestingly, NGC 2818/A is the only cluster-planetary combination that is currently believed to be truly associated. Although the status of NGC 2438 as a member of M46 is not known for certain, most indications are that the planetary is a foreground object. The relatively young age of M46 makes the possibility of one of it's member stars being the progenitor of the planetary nebula fairly remote. The NGC 2818 cluster, on the other hand, is older (perhaps as old as Billion years).>>
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<<[url=http://en.wikipedia.org/wiki/Pyxis][b]Pyxis[/b][/url] is a small and faint constellation in the southern sky. Its name is Latin for a mariner's compass (it should not be confused with Circinus, which represents a draftsman's compass). Pyxis is completely visible in latitudes south of 53 degrees north from January through March. Pyxis (Latin: box) was introduced by Nicolas Louis de Lacaille in the eighteenth century; he called it Pyxis Nautica, but the name was shortened. The constellation is located close to those forming the old constellation of Argo Navis (the ship Argo), and in the 19th century astronomer John Herschel suggested renaming Pyxis to 'Malus, the mast', but the suggestion was not followed.>>
http://www.astrosurf.com/antilhue/ngc_2818_in_pyxis.htm
----------------------------------------------
_The unique planetary nebula NGC 2818_ by Dufour, R. J.
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 287, Dec. 1, 1984, p. 341-352.
<<The planetary nebula NGC 2818, or PK 261 + 8 deg 1, is of special interest due to its apparent association with a Population I open cluster (of the same designation). The results of new observations of the nebula are presented, including interference-filter imagery, photoelectric photometry, and ground-based and IUE spectroscopy. Analysis of its composition based on new IUE and ground-based spectroscopy and model calculations of the very similar planetary nebula NGC 2440 suggests that NGC 2818 is a prototype of the He-rich and N-rich Type I group.
[b]NGC 2440 :
http://antwrp.gsfc.nasa.gov/apod/ap070215.html
http://antwrp.gsfc.nasa.gov/apod/ap060507.html[/b]
Compared to the composition of H II regions in the solar neighborhood, He is 60 percent overabundant, C is 0.3 dex lower, N is 1.0 dex higher, and O, Ne, Si, Cl, and Ar are essentially at comparable values. Analysis of kinematical and morphological data suggests that the nebula is probably associated with the star cluster (revised distance = 3.5 kpc). If so, then it is of exceptional size (radius approximately 1.1 pc), mass (greater than or equal to 0.6 solar mass), expansion velocity (52 + or - 3 km/s), and age (possibly as old as 22,000 yr). Some implications of the results regarding the masses of planetary-nebula progenitors, the nucleosynthesis processes in stars of intermediate mass, and the formation of planetary nebulae are also discussed.>>
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[quote] [b] http://www.skyhound.com/sh/archive/mar/NGC_2818.html [/b]
<<Where the heck have I been? That's what I found myself thinking as I looked at this wonderful planetary nebula embedded in an open cluster. These two objects both share an NGC number and some references use the designation 2818A to describe one or the other of the two. Planetary nebulae in open clusters make for a rare visual treat and the planetary that appears to lie in M46 is one of my all-time favorite objects.
[b]M46:
http://antwrp.gsfc.nasa.gov/apod/ap060910.html
http://antwrp.gsfc.nasa.gov/apod/ap990305.html[/b]
The planetary nebula NGC 2818 is relatively large and bright with interesting structure. This planetary is similar in size and brightness to the much better known "Bug" (NGC 6302) in Scorpius.
[b]NGC 6302:
http://apod.nasa.gov/apod/ap070429.html
http://antwrp.gsfc.nasa.gov/apod/ap980602.html[/b]
It's relatively high surface brightness takes magnification well. Look for the appearance of two separate, parallel, lobes that arc toward one another, nearly touching at the ends. Also look for a fainter outer envelope, particularly off each end, using averted vision. I didn't detect any color, but Steve Coe notes that "A few dark lanes are seen in the planetary at 165X, it is light green at all powers." Although NGC 2818 has a lower surface brightness than NGC 2438 (the PN in M46) it does compare favorably and its intriguing structure will surely bring me back again and again.
The NGC 2818 cluster is fairly faint, mostly made up of 11th to 14th magnitude stars. It is scattered and irregular and does not immediately jump out at you as a cluster of stars. It doesn't begin to compare to M46. Regardless, the many stars do make a nice backdrop for the planetary. Interestingly, NGC 2818/A is the only cluster-planetary combination that is currently believed to be truly associated. Although the status of NGC 2438 as a member of M46 is not known for certain, most indications are that the planetary is a foreground object. The relatively young age of M46 makes the possibility of one of it's member stars being the progenitor of the planetary nebula fairly remote. The NGC 2818 cluster, on the other hand, is older (perhaps as old as Billion years).>>[/quote]