Astronomy:AG Pegasi

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Short description: Star in the constellation Pegasus
AG Pegasi
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A visual band light curve for AG Pegasi. The inset plot shows the 2015 flare with an expanded time scale. Adapted Skopal from et al. (2012)[1] and Skopal et al. (2017)[2]
Observation data
Equinox J2000.0]] (ICRS)
Constellation Pegasus
Right ascension  21h 51m 01.97393s[3]
Declination +12° 37′ 32.1279″[3]
Apparent magnitude (V) 6.0 - 9.4[4]
Characteristics
Spectral type var + M3III[5]
B−V color index 1.158±0.031[6]
Variable type Symbiotic nova[2]
Astrometry
Radial velocity (Rv)−15.86±0.15[6] km/s
Proper motion (μ) RA: −1.382[3] mas/yr
Dec.: −1.728[3] mas/yr
Parallax (π)0.7358 ± 0.0354[3] mas
Distance2,600 or 4,100±160 ly
(800[7] or 1,270±50[8] pc)
Absolute magnitude (MV)/-1.0[7]
Orbit[9]
Period (P)818.2±1.6 days
Semi-major axis (a)2.5±0.1[7] AU
Eccentricity (e)0.110±0.039
Periastron epoch (T)2,446,812±48 HJD
Argument of periapsis (ω)
(primary)		112±22°
Semi-amplitude (K1)
(primary)		5.44±0.20 km/s
Details
White dwarf
Mass0.49[10] M☉
Radius0.06[11] R☉
Luminosity1,729[11] L☉
Surface gravity (log g)6.67[11] cgs
Temperature150,000[11] K
Red giant
Mass1.33[10] M☉
Radius151+9
−8[10] R☉
Luminosity1,150[7] L☉
Temperature3,500[12] K
Other designations
BD+11°4673, HD 207757, HIP 107848, SAO 107436[13]
Database references
SIMBADdata

AG Pegasi is a symbiotic binary star in the constellation Pegasus, composed of a red giant and white dwarf which are separated by 2.5 astronomical units and complete an orbit every 818 days. It is classified as a symbiotic nova; it has undergone one extremely slow nova outburst and a smaller outburst.

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.[14] 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 10,000 K in 1900,[7] with a likely radius 16 times that of the Sun,[15] before becoming a B-class star in 1920, then an O-class star in 1940, and finally a Wolf-Rayet star in 1970,[7] with a surface temperature of 95,000 K since 1978. It has shrunk to a 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.[15] AG Pegasi has been described as the slowest nova ever recorded,[7] with the hotter component having a constant bolometric luminosity for over 130 years from 1850 to 1980. By the late 20th century, it had 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 5,000 years before erupting. Both stars are ejecting material in stellar winds.[7] The resulting nebula contains material from both stars and is complex in nature.[16]

From 1997 until 2015, AG Pegasi entered a quiescent phase with no further change to its brightness; then the hot component increased in temperature, which caused the nebulosity around the stars to become more ionised and increase in brightness. The combination of the extremely slow nova and smaller outburst means that AG Pegasi is classed as a symbiotic nova.[2]

References

  1. ↑ Skopal, A.; Shugarov, S.; Vanko, M.; Dubovsky, P.; Peneva, S. P.; Semkov, E.; Wolf, M. (April 2012). "Recent photometry of symbiotic stars". Astronomische Nachrichten 333 (3): 242–255. doi:10.1002/asna.201111655. Bibcode: 2012AN....333..242S. 
  2. ↑ 2.0 2.1 2.2 Skopal, A; Shugarov, S. Yu; Sekeráš, M; Wolf, M; Tarasova, T. N; Teyssier, F; Fujii, M; Guarro, J et al. (2017). "New outburst of the symbiotic nova AG Pegasi after 165 yr". Astronomy & Astrophysics 604: A48. doi:10.1051/0004-6361/201629593. Bibcode: 2017A&A...604A..48S. 
  3. ↑ 3.0 3.1 3.2 3.3 Vallenari, A. et al. (2022). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy & Astrophysics. doi:10.1051/0004-6361/202243940  Gaia DR3 record for this source at VizieR.
  4. ↑ Samus, N. N. et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S 1: B/GCVS. Bibcode: 2009yCat....102025S. 
  5. ↑ 5.0 5.1 Kenyon, S. J.; Proga, D.; Keyes, C. D. (2001). "The Continuing Slow Decline of AG Pegasi". The Astronomical Journal 122 (1): 349–359. doi:10.1086/321107. Bibcode: 2001AJ....122..349K. 
  6. ↑ 6.0 6.1 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 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. doi:10.1086/116749. Bibcode: 1993AJ....106.1573K. 
  8. ↑ Bailer-Jones, C. A. L.; Rybizki, J.; Fouesneau, M.; Demleitner, M.; Andrae, R. (2021-03-01). "Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3". The Astronomical Journal 161 (3): 147. doi:10.3847/1538-3881/abd806. ISSN 0004-6256. Bibcode: 2021AJ....161..147B.  Data about this star can be seen here.
  9. ↑ Fekel, Francis C.; Joyce, Richard R.; Hinkle, Kenneth H.; Skrutskie, Michael F. (2000-03-01). "Infrared Spectroscopy of Symbiotic Stars. I. Orbits for Well-Known S-Type Systems". The Astronomical Journal 119 (3): 1375–1388. doi:10.1086/301260. ISSN 0004-6256. Bibcode: 2000AJ....119.1375F. 
  10. ↑ 10.0 10.1 10.2 Merc, Jaroslav; Boffin, Henri M. J. (2025-03-01). "Revisiting symbiotic binaries with interferometry - I. The PIONIER archival collection" (in en). Astronomy & Astrophysics 695: A61. doi:10.1051/0004-6361/202553789. ISSN 0004-6361. 
  11. ↑ 11.0 11.1 11.2 11.3 Sion, Edward M.; Godon, Patrick; Mikolajewska, Joanna; Katynski, Marcus (2019-04-05). "FUSE Spectroscopic Analysis of the Slowest Symbiotic Nova AG Peg During Quiescence" (in en). The Astrophysical Journal 874 (2): 178. doi:10.3847/1538-4357/ab0c0a. ISSN 0004-637X. Bibcode: 2019ApJ...874..178S. 
  12. ↑ Richichi, A.; Fabbroni, L.; Ragland, S.; Scholz, M. (1999-04-01). "A homogeneous temperature calibration for K and M giants with an extension to the coolest stars". Astronomy and Astrophysics 344: 511–520. ISSN 0004-6361. Bibcode: 1999A&A...344..511R. 
  13. ↑ "AG Peg". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=AG+Peg. 
  14. ↑ Boyarchuk, A.A. (1967). "The Nature of AG Pegasi". Soviet Astronomy 11 (1): 8–15. Bibcode: 1967SvA....11....8B. http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1967SvA....11....8B&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf. 
  15. ↑ 15.0 15.1 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. 
  16. ↑ Lü, G.; Zhu, C.; Han, Z.; Wang, Z. (2008). "Chemical Abundances in Symbiotic Stars". The Astrophysical Journal 683 (2): 990–1005. doi:10.1086/589876. Bibcode: 2008ApJ...683..990L. 



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