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}}</ref> The nebula is also designated "PGC 3517755" even through this type of designation is normally reserved for [[galaxies]].<ref name=cseligman/> To emphasize it is not actually a galaxy, quotation marks are usually used when referring to the nebula with this designation.
}}</ref> The nebula is also designated "PGC 3517755" even through this type of designation is normally reserved for [[galaxies]].<ref name=cseligman/> To emphasize it is not actually a galaxy, quotation marks are usually used when referring to the nebula with this designation.
Like many planetary nebulae, there is a [[star]] at the nebula's centre. It has a [[star magnitude|magnitude]] of +17.7 and exhibits a continious spectrum.<ref>{{cite web|url=http://cs.astronomy.com/asy/m/starclusters/491028.aspx|title=M46 + NGC 2438|accessdate=2019-11-01|publisher=cs.astronomy.com|date=2016-03-26}}</ref><ref name=seds/> The star, a [[white dwarf]], is one of the hottest stars ever observed with an estimated surface temperature of 75,000 K.<ref>{{cite web|url=http://www.kopernik.org/images/archive/n2438.htm|title=Planetary Nebula NGC 2438 in Puppis|accessdate=2019-11-01|publisher=kopernik.org|date=2000-03-13|author=George Normandin}}</ref> This central star is surrounded by a bright ring of diameter 1 light year and a much fainter halo of [[ionization|ionized]] [[gas]] with a diameter of 4.5 light years.<ref name=cseligman/><ref name=apod2011/> The fainter enveloping halo has a surface brightness around 1,000 dimmer than the inner region.<ref>
Like many planetary nebulae, there is a [[star]] at the nebula's centre. It has a [[star magnitude|magnitude]] of +17.7 and exhibits a continuous spectrum.<ref>{{cite web|url=http://cs.astronomy.com/asy/m/starclusters/491028.aspx|title=M46 + NGC 2438|accessdate=2019-11-01|publisher=cs.astronomy.com|date=2016-03-26}}</ref><ref name=seds/> The star, a [[white dwarf]], is one of the hottest stars ever observed with an estimated surface temperature of 75,000 K.<ref>{{cite web|url=http://www.kopernik.org/images/archive/n2438.htm|title=Planetary Nebula NGC 2438 in Puppis|accessdate=2019-11-01|publisher=kopernik.org|date=2000-03-13|author=George Normandin}}</ref> This central star is surrounded by a bright ring of diameter 1 light year and a much fainter halo of [[ionization|ionized]] [[gas]] with a diameter of 4.5 light years.<ref name=cseligman/><ref name=apod2011/> The fainter enveloping halo has a surface brightness around 1,000 dimmer than the inner region.<ref>
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{{cite journal
|last1=Oettl |first1=S.
|last1=Oettl |first1=S.