WR 1

WR 1 is a Wolf-Rayet star located around 6,000 light years away from Earth in the constellation of Cassiopeia. It is only a third larger than the sun, but due to a temperature over 100,000 K it is 250,000 times as luminous as the sun.

Not to be confused with WR-1.
WR 1
Observation data
Epoch 2000      Equinox 2000
Constellation Cassiopeia
Right ascension  00h 43m 28.39827s[1]
Declination +64° 45′ 35.4011″[1]
Apparent magnitude (V) 10.54[2]
Characteristics
Evolutionary stage Wolf-Rayet
Spectral type WN4-s[3]
U−B color index −0.24[4]
B−V color index +0.37[4]
Variable type WR[2]
Astrometry
Proper motion (μ) RA: −2.847±0.046[5] mas/yr
Dec.: −0.639±0.042[5] mas/yr
Parallax (π)0.2853 ± 0.0323[5] mas
Distanceapprox. 11,000 ly
(approx. 3,500 pc)
Absolute magnitude (MV)−4.74[3]
Details
Mass27[3] M☉
Radius2.26[3] R☉
Luminosity760,000[3] L☉
Temperature112,200[3] K
Rotational velocity (v sin i)6.5[6] km/s
Other designations
V863 Cas, BD+63° 83, HD 4004, HIP 3415
Database references
SIMBADdata

Although WR 1 has been recognised as a Wolf-Rayet star since the 19th century,[7] the WR 1 designation does not indicate that it was the first to be discovered. Ordered by right ascension, WR 1 is the first star in the Sixth Catalogue of galactic Wolf-Rayet stars.[8]

WR 1 is a member of the nitrogen sequence of WR stars and has a spectrum with HeII lines much stronger than HeI lines, and NV emission more than twice the strength of NIII, leading to the assignment of a WN4 spectral type. The spectrum has particularly wide HeII, leading to the equivalent classifications of WN4-b (for broad) or WN4-s (for strong). The spectrum also includes CIV and NIV, but no hydrogen lines at all.[9][10]

WR 1 is slightly variable and given the variable star designation V863 Cassiopeiae. The total amplitude of the variations is only 0.09 magnitudes at visual wavelengths. The variations are well-defined with a period of 16.9 days, but the light curve is not sinusoidal and its shape may vary.[11] The variations have been ascribed to a dense asymmetric stellar wind and co-rotating interacting regions in ejected material.[6]

It has been suggested that the variability and an infrared excess could be due to a cool companion, but WR 1 is now considered to be a single star.[10] The WN-b subclass of Wolf-Rayet star are generally thought to be all single, in contrast with the WN-A subclass which have narrow emission on a stronger continuum and are thought to be binary systems with a more conventional hot luminous star.[9]

WR 1 is a possible member of the Cassiopeia OB7 association[8] at a distance of around 1,800 pc,[3] although its Gaia parallax suggests it is more distant.[5] Interstellar extinction is calculated to be 2.1 magnitudes, and at 1,820 pc the bolometric luminosity would be 250,000 L☉. A temperature of 112,200 K is derived from fitting the spectrum, giving a radius of 2.26 R☉.[3]

References
  1. Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  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. Bibcode:2009yCat....102025S.
  3. Sota, A.; Maíz Apellániz, J.; Morrell, N. I.; Barbá, R. H.; Walborn, N. R.; Gamen, R. C.; Arias, J. I.; Alfaro, E. J.; Oskinova, L. M. (2019). "The Galactic WN stars revisited. Impact of Gaia distances on fundamental stellar parameters". Astronomy & Astrophysics. A57: 625. arXiv:1904.04687. Bibcode:2019A&A...625A..57H. doi:10.1051/0004-6361/201834850.
  4. Pyper, Diane M. (1966). "The Effective Temperatures of Wolf-Rayet Stars as Derived from Their U BV Color Indices Corrected for Emission". Astrophysical Journal. 144: 13. Bibcode:1966ApJ...144...13P. doi:10.1086/148587.
  5. 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. Gaia DR2 record for this source at VizieR.
  6. St-Louis, N. (2013). "Revealing the Asymmetry of the Wind of the Variable Wolf-Rayet Star WR1 (HD 4004) through Spectropolarization". The Astrophysical Journal. 777 (1): 9. arXiv:1308.5914. Bibcode:2013ApJ...777....9S. doi:10.1088/0004-637X/777/1/9.
  7. Campbell, W. W. (1894). "The Wolf-Rayet stars". Astronomy and Astro-Physics. 13: 448. Bibcode:1894AstAp..13..448C.
  8. Van Der Hucht, Karel A.; Conti, Peter S.; Lundström, Ingemar; Stenholm, Björn (1981). "The Sixth Catalogue of galactic Wolf-Rayet stars, their past and present". Space Science Reviews. 28 (3): 227–306. Bibcode:1981SSRv...28..227V. doi:10.1007/BF00173260.
  9. Smith, Lindsey F.; Shara, Michael M.; Moffat, Anthony F. J. (1996). "A three-dimensional classification for WN stars". Monthly Notices of the Royal Astronomical Society. 281 (1): 163–191. Bibcode:1996MNRAS.281..163S. doi:10.1093/mnras/281.1.163.
  10. Niedzielski, Andrzej (1998). "The Optical Spectrum of HD 4004 (WN4b). Evidence of Variability". Acta Astronomica. 48: 729. Bibcode:1998AcA....48..729N.
  11. Chené, A.-N.; St-Louis, N. (2010). "Large-scale Periodic Variability of the Wind of the Wolf-Rayet Star WR 1 (HD 4004)". The Astrophysical Journal. 716 (2): 929. arXiv:1004.4893. Bibcode:2010ApJ...716..929C. doi:10.1088/0004-637X/716/2/929.
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