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NGC 2438
NGC 2438 is a planetary nebula about 3,000 light years away in the constellation Puppis. It was discovered by William Herschel on March 19, 1786.〔(【引用サイトリンク】url=http://cseligman.com/text/atlas/ngc24.htm#2438 )〕
The planetary nebula NGC 2438 appears to lie within the cluster M46, but it is most likely unrelated since it does not share the cluster's radial velocity.〔Majaess D. J., Turner D., Lane D. (2007). (''In Search of Possible Associations between Planetary Nebulae and Open Clusters'' ), PASP, 119, 1349〕〔Kiss, L. L., Szabó, Gy. M., Balog, Z., Parker, Q. A., Frew, D. J. (2008). (''AAOmega radial velocities rule out current membership of the planetary nebula NGC 2438 in the open cluster M46'' ), MNRAS〕 The case is yet another example of a superposed pair, joining the famed case of NGC 2818.〔〔Mermilliod, J.-C., Clariá, J. J., Andersen, J., Piatti, A. E., Mayor, M. (2001). (''Red giants in open clusters. IX. NGC 2324, 2818, 3960 and 6259'' ), A&A〕
Long exposures have shown that this planetary nebula has an extended halo,〔(【引用サイトリンク】url=http://messier.seds.org/xtra/ngc/n2438.html )〕 while the more easily visible portion probably dates to the death of the red giant in its center.〔
==Central star==
The central star of this planetary nebula is a 17.7-magnitude white dwarf,〔 with surface temperature of about .〔(【引用サイトリンク】url=http://www.kopernik.org/images/archive/n2438.htm )〕 It is one of the hottest stars known.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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