S Monocerotis

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S Monocerotis
Observation data
Epoch J2000      Equinox J2000
Constellation Monoceros
Right ascension 06h 40m 58.6607s[1]
Declination +09° 53′ 44.715″[1]
Apparent magnitude (V) 4.66
Spectral type O7V + O9.5V[2]
U−B color index −1.034[3]
B−V color index −0.261[3]
Radial velocity (Rv) 33.2[4] km/s
Proper motion (μ) RA: –0.66[1] mas/yr
Dec.: –2.51[1] mas/yr
Parallax (π) 3.19 ± 0.73[1] mas
Distance 720[2] pc
Mass 59[2] M
Radius 9.3[5] R
Surface gravity (log g) 4.0[5] cgs
Temperature 35,427 ± 73[5] K
Rotational velocity (v sin i) 120[6] km/s
Other designations
15 Monocerotis, BD+10 1220, HD 47839, HIP 31978, HR 2456, SAO 114258.
Database references

S Monocerotis, also known as 15 Monocerotis, is a massive variable star system located in the constellation Monoceros.[7] It is a spectroscopic binary system with an orbital period of 74 years.[2] Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified.[8] It is a type O main sequence dwarf varying in between magnitude 4.2 and 4.6. The star lies at the base of the Christmas Tree Cluster in NGC 2264.

Physical data for the system is disputed. The Washington Double Star catalog reports it as having 8 components.[9] From orbital parameters and association with NGC 2264 it is given a distance of 720pc, but the Hipparcos parallax suggests less than half that.


  1. ^ a b c d e Perryman, M. A. C.; et al. (April 1997). "The HIPPARCOS Catalogue". Astronomy & Astrophysics 323: L49–L52. Bibcode:1997A&A...323L..49P. 
  2. ^ a b c d Cvetković, Z.; Vince, I.; Ninković, S. (2010). "A new orbit of binary 15 Monocerotis". New Astronomy 15 (3): 302. Bibcode:2010NewA...15..302C. doi:10.1016/j.newast.2009.09.002. 
  3. ^ a b Oja, T. (August 1985). "Photoelectric photometry of stars near the north Galactic pole. II". Astronomy and Astrophysics Supplement Series 61: 331–339. Bibcode:1985A&AS...61..331O. 
  4. ^ Wilson, Ralph Elmer (1953). General Catalogue of Stellar Radial Velocities. Washington: Carnegie Institution of Washington. Bibcode:1953QB901.W495..... 
  5. ^ a b c Underhill, A. B.; et al. (November 1979), "Effective temperatures, angular diameters, distances and linear radii for 160 O and B stars", Monthly Notices of the Royal Astronomical Society 189 (3): 601–605, Bibcode:1979MNRAS.189..601U, doi:10.1093/mnras/189.3.601 
  6. ^ Bernacca, P. L.; Perinotto, M. (1970). "A catalogue of stellar rotational velocities". Contributi Osservatorio Astronomico di Padova in Asiago 239 (1). Bibcode:1970CoAsi.239....1B. 
  7. ^ Heather Couper and Nigel Henbest (1999). Space Encyclopedia. Verona, Italy: Dorling Kindersley. p. 175. ISBN 0-7894-4708-8. 
  8. ^ Garrison, R. F. (December 1993), "Anchor Points for the MK System of Spectral Classification", Bulletin of the American Astronomical Society 25: 1319, Bibcode:1993AAS...183.1710G, retrieved 2012-02-04 
  9. ^ Worley, C. E.; Douglass, G. G. (1997). "The Washington Double Star Catalog (WDS, 1996.0)". Astronomy and Astrophysics Supplement Series 125 (3): 523. Bibcode:1997A&AS..125..523W. doi:10.1051/aas:1997239. 

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