AG Pegasi

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AG Pegasi

Observation data
Epoch J2000      Equinox J2000
Constellation Pegasus
Right ascension 21h 51m 01.97413s
Declination +12° 37′ 32.1218″
Apparent magnitude (V) var
Spectral type WN6+M3III
B−V color index 0.76
Variable type Symbiotic nova
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[1] pc
Absolute magnitude (MV) /-1.0[2]
AG Peghot
Mass 0.6[2] M
Radius 0.08-16[3] R
Luminosity 400-3,700 L
Surface gravity (log g) 6.0[1] cgs
Temperature 10,000K-100,000[2] K
AG Peggiant
Mass 2.5[2] M
Radius 85[2] R
Luminosity 1,150[2] L
Temperature 3,650[2] K
Other designations
BD+11°4673, HD 207757, HIP 107848, SAO 107436
Database references

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.[2]

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.[4] 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,[2] with a likely radius 16 times that of the Sun,[3] before becoming a B-class star in 1920, then an O-class star in 1940, and finally a Wolf-Rayet star in 1970,[2] 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.[3] AG Pegasi has been described as the slowest nova ever recorded,[2] 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.[5]

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.[2] The resulting nebula contains material from both stars and is complex in nature.[1]


  1. ^ a b c Lü, G.; Zhu, C.; Han, Z.; Wang, Z. (2008). "Chemical Abundances in Symbiotic Stars". The Astrophysical Journal 683 (2): 990. doi:10.1086/589876.  edit
  2. ^ a b c d e f g h i j k l Kenyon, S. J.; Mikolajewska, J.; Mikolajewski, M.; Polidan, R. S.; Slovak, M. H. (1993). "Evolution of the symbiotic binary system AG Pegasi - the slowest classical nova eruption ever recorded". The Astronomical Journal 106: 1573–98. Bibcode:1993AJ....106.1573K. doi:10.1086/116749.  edit
  3. ^ a b c Vogel, M.; Nussbaumer, H. (1994). "The hot wind in the symbiotic nova AG Pegasi". Astronomy and Astrophysics 282 (1): 145–55. Bibcode:1994A&A...284..145V. 
  4. ^ Boyarchuk, A.A. (1967). "The Nature of AG Pegasi". Soviet Astronomy 11 (1): 8–15. Bibcode:1967SvA....11....8B. 
  5. ^ Kenyon, S. J.; Proga, D.; Keyes, C. D. (2001). "The Continuing Slow Decline of AG Pegasi". The Astronomical Journal 122: 349. doi:10.1086/321107.  edit