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HD 179821
HD 179821 is a massive bright star in the constellation of Aquila, generally classified as a G-type yellow hypergiant of perhaps 30 solar masses at a distance from Earth of roughly . It is surrounded by a dust shell that contributes to a double-peaked spectral energy distribution. It is estimated the star has lost about 10% of its initial mass after being a red supergiant star just 1,600 years ago, and is a likely supernova candidate.
== Observations ==
HD 179821 has a cold detached dust shell that has been studied with the help of the Hubble Space Telescope. The shell is approximately circular in shape, has an inner diameter of ~3".3 corresponding to 20,000 AU at 6,000 pc, and an outer diameter of 5".7 or more, with the star 0".35 from the centre of the shell. The current mass loss is low, but during the formation of the shell it is estimated to have been , an exceptionally high rate.〔 Like its constellation neighbor and also hypergiant star IRC+10420, it is surrounded by an extended reflection nebula. Discovered at near-IR wavelength, this indicates a massive star and, as with the reflection nebula around IRC+10420, it may be masking a star hotter than the given G5 spectral type.
The distance is estimated to be around 6,000 parsecs and has a high luminosity of between 〔 and . It has a high radial velocity of . According to the studies of Jura ''et al'' (2001), the star may explode as a supernova in the next 100,000 years.〔
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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