S Orionis

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S Orionis
Observation data
Epoch J2000      Equinox J2000
Constellation Orion
Right ascension 05h 29m 00.8948s[1]
Declination −04° 41′ 32.748″[1]
Apparent magnitude (V) 7.2 - 14.0[2]
Evolutionary stage AGB[3]
Spectral type M6.5e - M9.5e[2]
U−B color index +0.15[4]
B−V color index +1.73[4]
Variable type Mira[2]
Proper motion (μ) RA: 14.77[1] mas/yr
Dec.: -10.87[1] mas/yr
Parallax (π) 0.89 ± 2.08[1] mas
Distance 480 ± 120[3] pc
Radius 411 - 498[3] R
Temperature 2,173[5] K
Other designations
S Ori, BD−04°1146, HD 36090, SAO 132163, HIP 25673
Database references

S Orionis is a red giant star in the constellation Orion.


Pulsations of S Orionis, showing dust production and masers (ESO)

S Orionis is a Mira variable that pulsates with a 420‑day cycle, and varies in radius from 2.0 to 2.3 astronomical units.[3]


S Orionis is listed in the Washington Double Star Catalog as a double star with a tenth magnitude companion 47" away. The companion is G0 star HD 294176.[6]

Circumstellar environment[edit]

S Orionis is surrounded by masers and dust condensed from its cool stellar wind. The size of the dust shells varies as the star pulsates and changes temperature, from around 8 AU to 10 AU across. The positions of the masers have been measured very accurately using VLBI.[3]


  1. ^ a b c d e Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  2. ^ 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. 
  3. ^ a b c d e Wittkowski, M.; Boboltz, D. A.; Ohnaka, K.; Driebe, T.; Scholz, M. (2007). "The Mira variable S Orionis: Relationships between the photosphere, molecular layer, dust shell, and SiO maser shell at 4 epochs". Astronomy and Astrophysics. 470: 191. Bibcode:2007A&A...470..191W. arXiv:0705.4614Freely accessible. doi:10.1051/0004-6361:20077168. 
  4. ^ a b Celis s., L. (1982). "Red variable stars. I - UBVRI photometry and photometric properties". Astronomical Journal. 87: 1791. Bibcode:1982AJ.....87.1791C. doi:10.1086/113268. 
  5. ^ McDonald, I.; Zijlstra, A. A.; Boyer, M. L. (2012). "Fundamental parameters and infrared excesses of Hipparcos stars". Monthly Notices of the Royal Astronomical Society. 427: 343. Bibcode:2012MNRAS.427..343M. doi:10.1111/j.1365-2966.2012.21873.x. 
  6. ^ Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.