AG Pegasi
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| Observation data Epoch J2000 Equinox J2000 |
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|---|---|
| Constellation | Pegasus |
| Right ascension | 21h 51m 01.97413s |
| Declination | +12° 37′ 32.1218″ |
| Apparent magnitude (V) | var |
| Characteristics | |
| Spectral type | var + M3III[1] |
| B−V color index | 0.76 |
| Variable type | Symbiotic nova |
| Astrometry | |
| Radial velocity (Rv) | −15.86 km/s |
| Proper motion (μ) | RA: -0.77 mas/yr Dec.: -1.80 mas/yr |
| Parallax (π) | -1.58 ± 1.04 mas |
| Distance | 1,000[2] pc |
| Absolute magnitude (MV) | /-1.0[3] |
| Details | |
| AG Peghot | |
| Mass | 0.6[3] M☉ |
| Radius | 0.08-16[4] R☉ |
| Luminosity | 400-3,700 L☉ |
| Surface gravity (log g) | 6.0[2] cgs |
| Temperature | 10,000K-100,000[3] K |
| AG Peggiant | |
| Mass | 2.5[3] M☉ |
| Radius | 85[3] R☉ |
| Luminosity | 1,150[3] L☉ |
| Temperature | 3,650[3] K |
| Other designations | |
| Database references | |
| SIMBAD | data |
AG Pegasi is a symbiotic binary star in the constellation Pegasus. It is a close binary composed of a red giant and white dwarf, estimated to be around 2.5 and 0.6 times the mass of the Sun respectively.[3]
Initially a magnitude 9 star, AG Pegasi brightened and peaked at an apparent magnitude of 6.0 around 1885 before gradually fading to magnitude 9 in the late 20th century. Its spectrum was noted by earlier observers to resemble P Cygni.[5] The spectrum of the hotter star has changed drastically over 160 years, leading investigators Scott Kenyon and colleagues to surmise that its hotter component, originally a white dwarf, accumulated enough material from the donor giant star to begin burning hydrogen and enlarge and brighten into an A-type white supergiant around 1850. It had this spectrum and an estimated surface temperature of around 10000 K in 1900,[3] with a likely radius 16 times that of the Sun,[4] before becoming a B-class star in 1920, then an O-class star in 1940, and finally a Wolf-Rayet star in 1970,[3] with a surface temperature of 95000 K since 1978. It has shrunk to star with a diameter 1.1 times that of the Sun in 1949, then 0.15 times in 1978 and 0.08 times that of the Sun in 1990.[4] AG Pegasi has been described as the slowest nova ever recorded,[3] with a constant bolometric luminosity of the hotter star over 130 years from 1850 to 1980. By the late 20th century, the hotter star has evolved into a hot subdwarf on its way to eventually returning to white dwarf status.[1]
Vogel and colleagues calculated the hotter star must have been accreting material from the red giant for around 5000 years before erupting. Both stars are ejecting material in stellar winds.[3] The resulting nebula contains material from both stars and is complex in nature.[2]
References
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