NGC 2440 is a planetary nebula, one of many in our galaxy. Its central star, HD 62166, is possibly the hottest known white dwarf, about 400,000°F(200,000°C). The nebula is situated in the constellation Puppis. It was discovered by William Herschel on March 4, 1790. He described it as "a beautiful planetary nebula of a considerable degree of brightness, not very well defined." The nebula is located about 1.23 kiloparsecs (3.79×1019 m) or about 4,000 light years from the Sun.
HD 62166 The central star HD 62166 has an exceptionally high surface temperature of about 200,000 kelvins and a luminosity 1,100 times that of the Sun. This dense star, with an estimated 0.6 solar mass and 0.028 solar radius, has an apparent magnitude of 17.5.
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Hubble Space Telescope reveals NGC 2440 on YouTube NASA Astronomy Picture of the Day: Planetary Nebula NGC 2440 (15 February 2007) NASA Astronomy Picture of the Day: NGC 2440: Cocoon of a New White Dwarf (7 May 2006) NASA Astronomy Picture of the Day: NGC 2440 Nucleus: The Hottest Star? (30 November 1995)