V Sagittae

V Sagittae
Location of V Sagittae (circled) in Sagitta
Observation data
Epoch J2000      Equinox ICRS
Constellation Sagitta
Right ascension 20h 20m 14.691s
Declination +21° 06′ 10.44″
Apparent magnitude (V) 8.6-13.9
Characteristics
Evolutionary stage White dwarf (primary)
Spectral type Be
Variable type eclipsing and cataclysmic
Astrometry
Proper motion (μ) RA: −2.133 mas/yr
Dec.: −6.489 mas/yr
Parallax (π)0.3310±0.0206 mas
Distance9,900 ± 600 ly
(3,000 ± 200 pc)
Absolute magnitude (MV)−2.2
Orbit
Period (P)12.34 hours
Semi-major axis (a)4.36 R☉
Inclination (i)65–80°
Semi-amplitude (K1)
(primary)		320 km/s
Semi-amplitude (K2)
(secondary)		85 km/s
Details
White dwarf (primary)
Mass1.0 M☉
Donor (secondary)
Mass0.8–1.0 M☉
Other designations
AAVSO 1015+20, V Sge, GSC 01643-01764
Database references
SIMBADdata

V Sagittae or V Sge is a cataclysmic variable in the constellation Sagitta. It is the only super soft X-ray source non-magnetic cataclysmic variable found so far. Lidiya Tseraskaya discovered the variability of this star, in 1902. It appeared with its variable star designation in Annie Jump Cannon's 1907 work Second catalogue of variable stars.

Characteristics

A visual band light curve for V Sagittae, adapted from Šimon and Mattei (1999)

There are two models that have been proposed to explain V Sagittae's properties. One says that the system is composed of a white dwarf accreting mass from a companion via an accretion disk, while the other model says that the system is composed of two hot stars (nearly) forming a contact binary. Both models have been disputed. Smak (2022) notes that the primary component shows similarities with Wolf-Rayet stars and the model with a white dwarf and its accretion disk does not explain many aspects of the system, including orbital period variations and mass loss from the primary, supporting a configuration with a Wolf-Rayet star and a main sequence star. However, a 2025 study by Hakala, Charles and Rodríguez-Gil found that the 'hot binary' model fails to explain multiple properties of V Sagittae, such as the system's variability, strong Hα emission and presence of stationary, double-peaked narrow emission lines, while the white dwarf model explains nearly all of them.

Material from the donor is accreting onto the primary 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. 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.

References

  1. 1 2 3 4 5 Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
  2. 1 2 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. 1 2 3 4 5 6 Hakala, Pasi; Charles, Phil; Rodríguez-Gil, Pablo (2025-10-06). "V Sge: supersoft source or exotic hot binary? – I. An X-Shooter campaign in the high state". Monthly Notices of the Royal Astronomical Society. 543 (3): 2058–2077. arXiv:2507.22637. Bibcode:2025MNRAS.543.2058H. doi:10.1093/mnras/staf1284. ISSN 0035-8711.
  4. ↑ Iriarte, B.; Chavira, E. (1955). "Nuevas estrellas de tipos espectrales tempranos con Hα en emisión entre l=339° y l=33°". Boletín de los Observatorios de Tonantzintla y Tacubaya. 2: 19. Bibcode:1955BOTT....2m..19I.
  5. 1 2 "V Sagittae technical details" (PDF). Retrieved 2021-10-03.
  6. 1 2 3 Smak, Jozef I.; Belczynski, K.; Zola, S. (2001). "V Sge: A Hot, Peculiar Binary System". Acta Astronomica. 51: 117. Bibcode:2001AcA....51..117S.
  7. ↑ Ryves, P. M. (May 1932). "A remarkable variable star (V Sagittæ)". Monthly Notices of the Royal Astronomical Society. 92: 715. Bibcode:1932MNRAS..92..715R. doi:10.1093/mnras/92.7.715.
  8. ↑ Cannon, Annie J. (1907). "Second catalogue of variable stars". Annals of Harvard College Observatory. 55: 1–94. Bibcode:1907AnHar..55....1C.
  9. ↑ 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.
  10. ↑ Smak, J. (2022). "On the Orbital Period and Models of V Sge". Acta Astronomica. 72 (1): 21–29. arXiv:2206.02177. Bibcode:2022AcA....72...21S. doi:10.32023/0001-5237/72.1.2. ISSN 0001-5237.
  11. ↑ "Binary star V Sagittae to explode as very bright nova by century's end". phys.org. Retrieved 2020-01-09.
  12. ↑ "CNN - Breaking News, Latest News and Videos". m.cnn.com. Archived from the original on 2020-01-13. Retrieved 2020-01-09.