V Sagittae

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V Sagittae
Vulpecula constellation map.svg
Red circle.svg
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]
Characteristics
Evolutionary stage White dwarf (primary) [3]
Spectral type Be [4]
Variable type eclipsing and cataclysmic [2]
Astrometry
Proper motion (μ)RA: −2.133 mas/yr [1]
Dec.: −6.489 mas/yr [1]
Parallax (π)0.3310±0.0206  mas [1]
Distance 9,900 ± 600  ly
(3,000 ± 200  pc)
Absolute magnitude  (MV)−2.2 [5]
Orbit
Period (P)12.34 [3] hours
Semi-major axis (a)4.36 R☉ [6]
Inclination (i)65–80 [3] °
Semi-amplitude (K1)
(primary)		320 [6]  km/s
Semi-amplitude (K2)
(secondary)		85 [6]  km/s
Details
White dwarf (primary)
Mass 1.0 [3]   M☉
Donor (secondary)
Mass 0.8–1.0 [3]   M☉
Other designations
AAVSO 1015+20, V Sge, GSC 01643-01764
Database references
SIMBAD data

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. [7] It appeared with its variable star designation in Annie Jump Cannon's 1907 work Second catalogue of variable stars. [8]

Characteristics

A visual band light curve for V Sagittae, adapted from Simon and Mattei (1999) VSgeLightCurve.png
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. [10] 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. [3]

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. [5] 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. [11] [12]

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.


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