V Sagittae

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]
Characteristics
Evolutionary stage	Wolf-Rayet star (A) [3] Main sequence (B) [3]
Spectral type	B1 [4]
Variable type	eclipsing and cataclysmic [2]
Astrometry
Proper motion (μ)	RA: −2.133 [1] mas/yr Dec.: −6.489 [1] mas/yr
Parallax (π)	0.3310±0.0206  mas [1]
Distance	9,900 ± 600  ly (3,000 ± 200  pc)
Absolute magnitude  (MV)	−2.2 [5]
Orbit [6]
Semi-major axis (a)	4.36 R☉
Inclination (i)	71°
Semi-amplitude (K1) (primary)	320 km/s
Semi-amplitude (K2) (secondary)	85 km/s
Details
Wolf-Rayet primary [3] (V Sge A)
Mass	0.9 [6]   M☉
Radius	1.2 [6]   R☉
Luminosity	30,000 [6]   L☉
Temperature	70,000 [6]   K
Donor [3] (V Sge B)
Mass	3.3 [6]   M☉
Radius	2.1 [6]   R☉
Temperature	12,000 [6]   K
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. The system is composed of a main sequence star of about 3.3 solar masses and a Wolf-Rayet star ^[3] of about 0.9 solar masses. ^[7] V Sge is the only super soft X-ray source nonmagnetic cataclysmic variable found so far.

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

Material from the larger star is accreting onto the WR star 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. ^{[7] [9]}

Component A was long thought to be a white dwarf, but the primary component show similarities with a 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. ^[3]

References

1. 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. 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. 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.
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. "V Sagittae technical details" (PDF). Retrieved 2021-10-03.
6. Smak, Jozef I.; Belczynski, K.; Zola, S. (2001). "V Sge: A Hot, Peculiar Binary System". Acta Astronomica. 51: 117. Bibcode:2001AcA....51..117S.
7. "Binary star V Sagittae to explode as very bright nova by century's end". phys.org. Retrieved 2020-01-09.
8. 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 .
9. "CNN - Breaking News, Latest News and Videos". m.cnn.com. Archived from the original on 2020-01-13. Retrieved 2020-01-09.