  | |
| 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 | |
| Spectral type | B1 [3] |
| 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 [4] |
| Orbit [5] | |
| 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 | |
| White dwarf | |
| Mass | 0.9 [5] M☉ |
| Radius | 1.2 [5] R☉ |
| Luminosity | 30,000 [5] L☉ |
| Temperature | 70,000 [5] K |
| Donor | |
| Mass | 3.3 [5] M☉ |
| Radius | 2.1 [5] R☉ |
| Temperature | 12,000 [5] 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 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, [6] and V Sge is the only super soft X-ray source nonmagnetic cataclysmic variable found so far.
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. [4] 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. [6] [8]
