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HD 179821
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HD 179821
HD 179821 or V1427 Aquilae is either a post-red supergiant yellow hypergiant or a post-AGB yellow supergiant star in the constellation of Aquila, surrounded by a detached dust shell. It is a semi-regular variable nearing the end of its life.
HD 179821 was first catalogued as an unremarkable 8th magnitude star at the start of the 20th century. It was later listed as a spectral standard G4 0-Ia, indicating a highly luminous star type now known as a hypergiant.
It was first considered notable for its infrared excess and double-peaked spectral energy distribution in the infrared. These were considered to be indicators of surrounding dust and HD 179821 was identified as a possible protoplanetary nebula. Variability was also detected.
High resolution spectroscopic studies and modern space-based observations have revealed an unusual chemical makeup and a hollow spherical dust shell, but haven't fully resolved whether HD 179821 is a highly luminous yellow hypergiant or a dimmer, lower-mass post-AGB star.
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 4×10−4 M☉/yr, an exceptionally high rate being comparable to that of the archetypical OH/IR red supergiant, VY Canis Majoris. 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.
It is that which 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.
The distance was once estimated to be around 6,000 parsecs. It has a high luminosity of between 1.26×105 and 2.95×105 L⊙ and a radius of between 400 and 450 R☉. It has a high radial velocity of +100 km/s. According to the studies of Jura et al (2001), the star may explode as a supernova in the next 100,000 years.
HD 179821 is a semiregular variable star with the variable star designation V1427 Aquilae. Between 1899 and 1989, its photographic apparent magnitude varied erratically between about magnitudes 9 and 10, although coverage is not complete and some larger variations may have been missed. It then varied by no more than 0.1 magnitudes until 2009, at a visual magnitude around 8.1.
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HD 179821
HD 179821 or V1427 Aquilae is either a post-red supergiant yellow hypergiant or a post-AGB yellow supergiant star in the constellation of Aquila, surrounded by a detached dust shell. It is a semi-regular variable nearing the end of its life.
HD 179821 was first catalogued as an unremarkable 8th magnitude star at the start of the 20th century. It was later listed as a spectral standard G4 0-Ia, indicating a highly luminous star type now known as a hypergiant.
It was first considered notable for its infrared excess and double-peaked spectral energy distribution in the infrared. These were considered to be indicators of surrounding dust and HD 179821 was identified as a possible protoplanetary nebula. Variability was also detected.
High resolution spectroscopic studies and modern space-based observations have revealed an unusual chemical makeup and a hollow spherical dust shell, but haven't fully resolved whether HD 179821 is a highly luminous yellow hypergiant or a dimmer, lower-mass post-AGB star.
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 4×10−4 M☉/yr, an exceptionally high rate being comparable to that of the archetypical OH/IR red supergiant, VY Canis Majoris. 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.
It is that which 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.
The distance was once estimated to be around 6,000 parsecs. It has a high luminosity of between 1.26×105 and 2.95×105 L⊙ and a radius of between 400 and 450 R☉. It has a high radial velocity of +100 km/s. According to the studies of Jura et al (2001), the star may explode as a supernova in the next 100,000 years.
HD 179821 is a semiregular variable star with the variable star designation V1427 Aquilae. Between 1899 and 1989, its photographic apparent magnitude varied erratically between about magnitudes 9 and 10, although coverage is not complete and some larger variations may have been missed. It then varied by no more than 0.1 magnitudes until 2009, at a visual magnitude around 8.1.
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