BW Vulpeculae

BW Vulpeculae or BW Vul, is a variable star in the northern constellation of Vulpecula. It is near the lower limit of visibility to the naked eye with a typical apparent visual magnitude of 6.54.[2] Based on an annual parallax shift of 1.15 mas,[1] 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.[7]

BW Vulpeculae
Observation data
Epoch J2000      Equinox J2000
Constellation Vulpecula
Right ascension  20h 54m 22.39491s[1]
Declination +28° 31′ 19.1827″[1]
Apparent magnitude (V) 6.54[2] (6.44 – 6.68)[3]
Characteristics
Spectral type B2 IIIv[4]
U−B color index −0.147±0.011[5]
Variable type β Cep[6]
Astrometry
Radial velocity (Rv)−6.1±3.0[7] km/s
Proper motion (μ) RA: +0.437[1] mas/yr
Dec.: −4.981[1] mas/yr
Parallax (π)1.1494 ± 0.0652[1] mas
Distance2,800 ± 200 ly
(870 ± 50 pc)
Absolute magnitude (MV)−2.47[8]
Details
Mass6.8±0.1[9] or 11−14[10] M☉
Luminosity515.14[5] L☉
Surface gravity (log g)3.71[11] cgs
Temperature23,014+919
−883[11] K
Metallicity [Fe/H]0.07±0.12[11] dex
Rotational velocity (v sin i)24±6[2] km/s
Age3.4±2.5[9] Myr
Other designations
AAVSO 2050+28, BW Vul, BD+27° 3909, HD 199140, HIP 103191, HR 8007, SAO 89265[12]
Database references
SIMBADdata

This is a B-type giant star with a stellar classification of B2 IIIv,[4] 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,[10] although Tetzlaff et al. (2011) gives a mass of just 6.8 M☉.[9] It is about 3.4[9] million years old and is spinning with a projected rotational velocity of 24 km/s.[2] The star is typically radiating 515[5] times the Sun's luminosity from its photosphere at an effective temperature of 23,014 K.[11]

The variability of this star was announced in 1937, at the 58th Meeting of the American Astronomical Society by Canadian astronomer, Robert Methven Petrie.[13] It is a Beta Cephei variable that ranges between magnitudes 6.44 and 6.68 over a period of 4.8 hours.[3] For unknown reasons, the periodicity of the star has undergone sudden changes, followed by long periods of stability.[14] BW Vul is one of the most extreme β Cephei stars in terms of variability of light and radial velocity.[2][15] This is hypothesized as being due to the star's relatively high metallicity, meaning the abundance of elements other than hydrogen and helium.[10] 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.[15]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051.
  2. Stankov, A.; et al. (September 2003). "Abundances and radial velocity analysis of BW Vulpeculae". Astronomy and Astrophysics. 408: 1077–1086. Bibcode:2003A&A...408.1077S. doi:10.1051/0004-6361:20031005.
  3. Otero, Sebastian Alberto (21 November 2011). "BW Vulpeculae". AAVSO Website. American Association of Variable Star Observers. Retrieved 2 August 2015.
  4. Lynds, C. R. (September 1959). "The light-variability of early B giants". Astrophysical Journal. 130: 577. Bibcode:1959ApJ...130..577L. doi:10.1086/146747.
  5. Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters. 38 (5): 331. arXiv:1108.4971. Bibcode:2012AstL...38..331A. doi:10.1134/S1063773712050015.
  6. Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085.
  7. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
  8. Gontcharov, G. A. (November 2012). "Spatial distribution and kinematics of OB stars". Astronomy Letters. 38 (11): 694–706. arXiv:1606.09028. Bibcode:2012AstL...38..694G. doi:10.1134/S1063773712110035.
  9. Tetzlaff, N.; et al. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x.
  10. Fokin, A.; et al. (November 2004). "Hydrodynamic models for β Cephei variables. I. BW Vulpeculae revisited". Astronomy and Astrophysics. 426: 687–693. Bibcode:2004A&A...426..687F. doi:10.1051/0004-6361:20040418.
  11. Niemczura, E.; Daszyńska-Daszkiewicz, J. (April 2005). "Metallicities of the β Cephei stars from low-resolution ultraviolet spectra". Astronomy and Astrophysics. 433 (2): 659–669. arXiv:astro-ph/0410440. Bibcode:2005A&A...433..659N. doi:10.1051/0004-6361:20040396.. Note: value taken from [m/H].
  12. "BW Vul". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved September 7, 2018.
  13. Petrie, R. M. (1939). "A new Beta Canis Majoris-type star". Publications of the American Astronomical Society. 9: 53. Bibcode:1939PAAS....9Q..53P.
  14. Odell, A. P. (August 2012). "Period variation in BW Vulpeculae redux". Astronomy & Astrophysics. 544: 4. arXiv:1205.5996. Bibcode:2012A&A...544A..28O. doi:10.1051/0004-6361/201219418. A28.
  15. Smith, Myron A.; et al. (December 2005). "Far-Ultraviolet and Optical Observations of BW Vulpeculae". The Astrophysical Journal. 634 (2): 1300–1310. Bibcode:2005ApJ...634.1300S. doi:10.1086/497026.
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