| |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Vulpecula |
| Right ascension | 20h54m 22.39491s[2] |
| Declination | +28° 31′ 19.1827″[2] |
| Apparent magnitude (V) | 6.54[3] (6.44 – 6.68)[4] |
| Characteristics | |
| Spectral type | B2 IIIv[5] |
| U−B color index | −0.147±0.011[6] |
| Variable type | β Cep[7] |
| Astrometry | |
| Radial velocity (Rv) | −6.1±3.0[8] km/s |
| Proper motion (μ) | RA: +0.437[2] mas/yr Dec.: −4.981[2] mas/yr |
| Parallax (π) | 1.1494 ± 0.0652 mas[2] |
| Distance | 2,800 ± 200 ly (870 ± 50 pc) |
| Absolute magnitude (MV) | −2.47[9] |
| Details | |
| Mass | 6.8±0.1[10] or 11−14[11] M☉ |
| Luminosity | 515.14[6] L☉ |
| Surface gravity (log g) | 3.71[12] cgs |
| Temperature | 23,014+919 −883[12] K |
| Metallicity [Fe/H] | 0.07±0.12[12] dex |
| Rotational velocity (v sin i) | 24±6[3] km/s |
| Age | 3.4±2.5[10] Myr |
| Other designations | |
AAVSO 2050+28, BW Vul, BD+27° 3909, HD 199140, HIP 103191, HR 8007, SAO 89265[13] | |
| Database references | |
| SIMBAD | data |
BW VulpeculaeorBW Vul, is a variable star in the northern constellationofVulpecula. It is near the lower limit of visibility to the naked eye with a typical apparent visual magnitude of 6.54.[3] Based on an annual parallax shiftof1.15 mas,[2] the distance to BW Vul is about 2,800 light years. It is moving closer to the Earth with a baseline heliocentric radial velocity of around −6 km/s.[8]
This is a B-type giant star with a stellar classification of B2 IIIv,[5] where the 'v' suffix indicates variability in spectral features. Various authors have printed mass estimates ranging from 11 to 14 times the mass of the Sun,[11] although Tetzlaff et al. (2011) gives a mass of just 6.8 M☉.[10] It is about 3.4[10] million years old and is spinning with a projected rotational velocity of 24 km/s.[3] The star is typically radiating 515[6] times the Sun's luminosity from its photosphere at an effective temperature of 23,014 K.[12]
The variability of this star was announced in 1937, at the 58th Meeting of the American Astronomical Society by Canadian astronomer, Robert Methven Petrie.[14] It is a Beta Cephei variable that ranges between magnitudes 6.44 and 6.68 over a period of 4.8 hours.[4] For unknown reasons, the periodicity of the star has undergone sudden changes, followed by long periods of stability.[15] BW Vul is one of the most extreme β Cephei stars in terms of variability of light and radial velocity.[3][16] This is hypothesized as being due to the star's relatively high metallicity, meaning the abundance of elements other than hydrogen and helium.[11] A distinctive feature of its radial velocity cycle is a unique "standstill" feature, which is caused by a shockwave generated by infall of material from a previous cycle.[16]
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