V Sagittae or V Sge is a cataclysmic variable in the constellation Sagitta. The system is composed of a main sequence star of about 3.3 solar masses and a white dwarf of about 0.9 solar masses; the fact that the white dwarf is less massive than its companion is highly unusual for a cataclysmic variable,[5] and V Sge is the only super soft X-ray source nonmagnetic cataclysmic variable found so far.

V Sagittae
Location of V Sagittae (circled) in Sagitta
Observation data
Epoch J2000      Equinox J2000
Constellation Sagitta
Right ascension 20h 20m 14.691s[1]
Declination +21° 06′ 10.44″[1]
Apparent magnitude (V) 8.6-13.9[2]
Variable type eclipsing and cataclysmic[2]
Proper motion (μ) RA: −2.052[1] mas/yr
Dec.: −6.485[1] mas/yr
Parallax (π)0.4190 ± 0.0320 mas[1]
Distance7,800 ± 600 ly
(2,400 ± 200 pc)
Absolute magnitude (MV)−2.2[3]
Semi-major axis (a)4.36 R
Inclination (i)71°
Semi-amplitude (K1)
320 km/s
Semi-amplitude (K2)
85 km/s
Mass0.9[4] M
Radius1.2[4] R
Luminosity30,000[4] L
Temperature70,000[4] K
Mass3.3[4] M
Radius2.1[4] R
Temperature12,000[4] K
Other designations
AAVSO 1015+20, V Sge, GSC 01643-01764
Database references
A visual band light curve for V Sagittae, adapted from Šimon and Mattei (1999)[6]

Material from the larger star is accreting onto the white dwarf at an exponentially increasing rate, generating a huge stellar wind. The doubling time for the accretion rate, and hence for the system luminosity, is about 89±11 years.[3] It is predicted that the system will erupt as a nova some time between 2067 and 2099, at which point it will become one of the brightest stars in the sky.[5][7]


  1. ^ a b c d e Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. ^ a b Samus, N. N.; Durlevich, O. V.; 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.
  3. ^ a b "V Sagittae technical details" (PDF). Retrieved 2021-10-03.
  4. ^ a b c d e f g h Smak, Jozef I.; Belczynski, K.; Zola, S. (2001). "V Sge: A Hot, Peculiar Binary System". Acta Astronomica. 51: 117. Bibcode:2001AcA....51..117S.
  5. ^ a b "Binary star V Sagittae to explode as very bright nova by century's end". phys.org. Retrieved 2020-01-09.
  6. ^ Šimon, V.; Mattei, J. A. (October 1999). "The peculiar binary V Sagittae: Properties of its long-term light changes". Astronomy and Astrophysics Supplement Series. 139: 75–88. Bibcode:1999A&AS..139...75S. doi:10.1051/aas:1999381.
  7. ^ "CNN - Breaking News, Latest News and Videos". m.cnn.com. Archived from the original on 2020-01-13. Retrieved 2020-01-09.