W Orionis
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Right ascension 05h 05m 23.72142s[1]
Declination +01° 10′ 39.4512″[1]
Apparent magnitude (V) 4.4 - 6.9[2]
Evolutionary stage AGB
Spectral type C-N5 C25.5[3] (C5,4(N5)[4])
U−B color index +6.84[5]
B−V color index +3.42[5]
Variable type SRb[4]
Radial velocity (Rv)+16.50[6] km/s
Proper motion (μ) RA: +7.5[1] mas/yr
Dec.: -1.4[1] mas/yr
Parallax (π)2.65 ± 0.95[1] mas
Distanceapprox. 1,200 ly
(approx. 400 pc)
Absolute magnitude (MV)−5.76[7]
Mass1-2[8] M
Radius406[8] R
Luminosity6,761[8] L
Surface gravity (log g)−0.60[8] cgs
Temperature2,600[8] K
Metallicity [Fe/H]0.0[8] dex
Other designations
W Ori, BD−00°939, HD 32736, HIP 23680
Database references

W Orionis is a carbon star in the constellation Orion, approximately 400 parsecs (1,300 ly) away. It varies regularly in brightness between extremes of magnitude 4.4 and 6.9 roughly every 7 months.


W Orionis is a semiregular variable with an approximately 212‑day cycle.[4] A long secondary period of 2,450 days has also been reported.[9]


The angular diameter of W Orionis has been measured using interferometry and a value of 9.7 mas is found. Although it is known to be a pulsating variable star, no changes in the diameter were seen.[8]

Technetium has not been detected in W Orionis, an unexpected result since this s-process element should be dredged up in all thermally-pulsating AGB stars and especially in carbon stars.[8]


  1. ^ a b c d e 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. S2CID 18759600.
  2. ^ Watson, C. L; Henden, A. A; Price, A (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25. 25: 47. Bibcode:2006SASS...25...47W.
  3. ^ Barnbaum, Cecilia; Stone, Remington P. S; Keenan, Philip C (1996). "A Moderate-Resolution Spectral Atlas of Carbon Stars: R, J, N, CH, and Barium Stars". Astrophysical Journal Supplement. 105: 419. Bibcode:1996ApJS..105..419B. doi:10.1086/192323.
  4. ^ a b c 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.
  5. ^ a b Ducati, J. R (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
  6. ^ Gontcharov, G. A (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. S2CID 119231169.
  7. ^ Guandalini, R; Cristallo, S (2013). "Luminosities of carbon-rich asymptotic giant branch stars in the Milky Way". Astronomy & Astrophysics. 555: A120. arXiv:1305.4203. Bibcode:2013A&A...555A.120G. doi:10.1051/0004-6361/201321225. S2CID 54918450.
  8. ^ a b c d e f g h Cruzalèbes, P; Jorissen, A; Rabbia, Y; Sacuto, S; Chiavassa, A; Pasquato, E; Plez, B; Eriksson, K; Spang, A; Chesneau, O (2013). "Fundamental parameters of 16 late-type stars derived from their angular diameter measured with VLTI/AMBER". Monthly Notices of the Royal Astronomical Society. 434 (1): 437–450. arXiv:1306.3288. Bibcode:2013MNRAS.434..437C. doi:10.1093/mnras/stt1037. S2CID 49573767.
  9. ^ Olivier, E. A; Wood, P. R (2003). "On the Origin of Long Secondary Periods in Semiregular Variables". The Astrophysical Journal. 584 (2): 1035. Bibcode:2003ApJ...584.1035O. doi:10.1086/345715.