Vela X-1

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Vela X-1
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Vela
Right ascension 09h 02m 06.860s
Declination −40° 33′ 16.91″
Spectral type B0.5Ib
Apparent magnitude (B) 7.301
Apparent magnitude (V) 6.926
Apparent magnitude (J) 5.833±0.020
Apparent magnitude (H) 5.705±0.034
Apparent magnitude (K) 5.596±0.024
U−B color index -0.51
B−V color index 0.50
Variable type Complex
Proper motion (μ) RA: −5.81 mas/yr
Dec.: 8.25 mas/yr
Distance 6200±650 ly
(1900±200 pc)
Mass 1.88
(neutron star), ~18 (supergiant) M
Radius ~11.2 R
Luminosity 112,000 (supergiant) L
Temperature 31,500 (supergiant) K
Metallicity ?
Rotation 8.964 days (supergiant)
Age ? years
Other designations
Supergiant component: GP Vel, HD 77581, SAO 220767, HIP 44368, CPD-40°3072, CD-40°4838;
X-ray component: 1XRS 09002-403, 1RXS J090207.0-403311, 4U 0900-40
Data sources:
Hipparcos Catalogue,
GCVS (4.2),

Vela X-1 is a pulsing, eclipsing high-mass X-ray binary (HMXB) system, associated with the Uhuru source 4U 0900-40 and the supergiant star HD 77581. The X-ray emission of the neutron star is caused by the capture and accretion of matter from the stellar wind of the supergiant companion. Vela X-1 is the prototypical detached HMXB.[4]

The orbital period of the system is 8.964 days, with the neutron star being eclipsed for about two days of each orbit by HD 77581. The spin period of the neutron star is about 283 seconds, and gives rise to strong X-ray pulsations. The mass of the pulsar is estimated to be at least 1.88±0.13 solar masses.[5]


Long term monitoring of the spin period shows small random increases and decreases over time similar to a random walk.[6] The accreting matter causes the random spin period changes.


Vela X-1 should not be confused with the isolated radio pulsar, Vela Pulsar, which is a very different kind of object. Vela is associated with a very strong 100 MeV gamma-ray source, which corresponds to a rather weak Uhuru X-ray source, 4U 0833-45.

See also[edit]


  1. ^ "HD 77581". SIMBAD. Centre de données astronomiques de Strasbourg. 
  2. ^ Klare, G.; Neckel, T. (1977). "UBV, Hβ and polarization measurements of 1660 southern OB stars". Astronomy and Astrophysics Supplement. 27: 215. Bibcode:1977A&AS...27..215K. 
  3. ^ Sadakane, K.; et al. (1985). "Ultraviolet spectroscopic observations of HD 77581 (Vela X-1 = 4U 0900-40)". The Astrophysical Journal. 288: 284. Bibcode:1985ApJ...288..284S. doi:10.1086/162791. 
  4. ^ Mauche, C. W.; Liedahl, D. A.; Akiyama, S.; Plewa, T. (2007). "Hydrodynamic and Spectral Simulations of HMXB Winds". Progress of Theoretical Physics Supplement. 169: 196. arXiv:0704.0237free to read. Bibcode:2007PThPS.169..196M. doi:10.1143/PTPS.169.196. 
  5. ^ Quaintrell, H.; et al. (2003). "The mass of the neutron star in Vela X-1 and tidally induced non-radial oscillations in GP Vel". Astronomy and Astrophysics. 401: 313. arXiv:astro-ph/0301243free to read. Bibcode:2003A&A...401..313Q. doi:10.1051/0004-6361:20030120. 
  6. ^ Bildsten, L.; et al. (1997). "Observations of Accreting Pulsars". The Astrophysical Journal Supplement Series. 113 (2): 367. arXiv:astro-ph/9707125free to read. Bibcode:1997ApJS..113..367B. doi:10.1086/313060. 

External links[edit]

Coordinates: Sky map 09h 02m 06.860s, −40° 33′ 16.91″