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S Monocerotis, also known as 15 Monocerotis, is a massive multiple and variable star system located in the constellation Monoceros. It is the brightest star in the Christmas Tree open cluster in the area catalogued as NGC 2264.

S Monocerotis

S Monocereotis lies in NGC 2264 at the very northern edge of Monoceros.
Observation data
Epoch J2000      Equinox J2000
Constellation Monoceros
A
Right ascension 06h 40m 58.656s[1]
Declination +09° 53′ 44.71″[1]
Apparent magnitude (V) 4.66[2] (4.62 - 4.68[3]) + 5.90[2]
B
Right ascension 06h 40m 58.566s[1]
Declination +09° 53′ 42.20″[1]
Apparent magnitude (V) 7.830[1]
Characteristics
Spectral type O7V((f))zvar[4] + O9.5Vn[5] + B2V[6]
U−B color index −1.034[7]
B−V color index −0.261[7]
Variable type Ia[3]
Astrometry
A
Radial velocity (Rv)22.00[8] km/s
Proper motion (μ) RA: −2.61[9] mas/yr
Dec.: −1.61[9] mas/yr
Parallax (π)3.55 ± 0.50 mas[9]
Distance720[5] pc
Absolute magnitude (MV)−5.21[10]
B
Proper motion (μ) RA: −1.971[11] mas/yr
Dec.: −4.225[11] mas/yr
Parallax (π)1.4019 ± 0.0984 mas[11]
Distance2,300 ± 200 ly
(710 ± 50 pc)
C
Proper motion (μ) RA: −1.464[12] mas/yr
Dec.: −2.746[12] mas/yr
Parallax (π)1.5438 ± 0.0394 mas[12]
Distance2,110 ± 50 ly
(650 ± 20 pc)
Orbit[13]
PrimaryAa
CompanionAb
Period (P)108±12 yr
Semi-major axis (a)112.5±6 mas
Eccentricity (e)0.770+0.023
−0.030
Inclination (i)47±2°
Longitude of the node (Ω)60±3°
Periastron epoch (T)B 1996.05+0.15
−0.10
Argument of periastron (ω)
(secondary)		63±4°
Details
Aa
Mass29.1[2] M☉
Radius9.9[14] R☉
Luminosity214,000[14] L☉
Surface gravity (log g)4.5[15] cgs
Temperature38,500[14] K
Rotational velocity (v sin i)120[16] km/s
Ab
Mass21.3[2] M☉
Age3.1[17] Myr
Other designations
15 Monocerotis, HD 47839, HIP 31978, HR 2456, SAO 114258, BD+10°1220
Database references
SIMBADdata
ARICNSdata
NGC 2264 including the Cone Nebula and the Christmas Tree Cluster (upside down in this image) with S Monocerotis at the very top of the image (and the base of the Christmas tree)
NGC 2264 including the Cone Nebula and the Christmas Tree Cluster (upside down in this image) with S Monocerotis at the very top of the image (and the base of the Christmas tree)

S Monocerotis is found within an open cluster and the Washington Double Star Catalog lists many companion stars.[18] The closest and brightest is S Mon B, magnitude 7.8 and 3 arcseconds away. It is classified as B2 main sequence star with a mass of 7.31 M☉. Designated component C is an 11th-magnitude B8V star.[6] The cluster contains another dozen or so 9th and 10th magnitude stars and many fainter stars.

S Monocerotis A is a spectroscopic binary system with an eccentric orbit of about 112 years.[13] Since 1943, the spectrum of this star has served as the MK standard for O7 by which other stars are classified.[19] It is also an irregular variable star with a range of less than a tenth of a magnitude. The orbital parameters can be used to derive the masses of the two stars, giving 31 M☉ and 11 M☉.[6]

The distance to S Monocerotis and NGC 2264 has been derived in various ways, including dynamical parallax and isochrone fitting. These consistently give estimates of 700 - 900 parsecs, although this is double the likely distance derived from the Hipparcos parallax measurements.[9] Gaia Early Data Release 3 contains parallaxes for the companions components B and C of 1.4 mas and 1.5 mas respectively, consistent with the expected distance to the cluster.


References


  1. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H. doi:10.1888/0333750888/2862. ISBN 0333750888.
  2. Cvetkovc, Zorica; Vince, Istvan; Ninkovic, Slobodan (2008). "Orbit of Binary 15 Monocerotis". arXiv:0804.0698 [astro-ph].
  3. 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.
  4. Sota, A.; Maíz Apellániz, J.; Walborn, N. R.; Alfaro, E. J.; Barbá, R. H.; Morrell, N. I.; Gamen, R. C.; Arias, J. I. (2011). "The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-violet at R ~ 2500". The Astrophysical Journal Supplement. 193 (2): 24. arXiv:1101.4002. Bibcode:2011ApJS..193...24S. doi:10.1088/0067-0049/193/2/24. S2CID 119248206.
  5. Cvetković, Z.; Vince, I.; Ninković, S. (2010). "A new orbit of binary 15 Monocerotis". New Astronomy. 15 (3): 302–306. Bibcode:2010NewA...15..302C. doi:10.1016/j.newast.2009.09.002.
  6. Tokovinin, A. A. (1997). "MSC - a catalogue of physical multiple stars". Astronomy and Astrophysics Supplement Series. 124: 75–84. Bibcode:1997A&AS..124...75T. doi:10.1051/aas:1997181.
  7. 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.
  8. Pourbaix, D.; Tokovinin, A. A.; Batten, A. H.; Fekel, F. C.; Hartkopf, W. I.; Levato, H.; Morrell, N. I.; Torres, G.; Udry, S. (2004). "SB9: The ninth catalogue of spectroscopic binary orbits". Astronomy and Astrophysics. 424 (2): 727–732. arXiv:astro-ph/0406573. Bibcode:2004A&A...424..727P. doi:10.1051/0004-6361:20041213. S2CID 119387088.
  9. 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.
  10. Feinstein, A.; Vazquez, R. A.; Benvenuto, O. G. (1986). "Of-stars in young open clusters". Astronomy and Astrophysics. 159: 223. Bibcode:1986A&A...159..223F.
  11. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  12. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
  13. Maíz Apellániz, J. (2019). "Gaia DR2 distances to Collinder 419 and NGC 2264 and new astrometric orbits for HD 193 322 Aa,Ab and 15 Mon Aa,Ab". Astronomy and Astrophysics. 630: A119. arXiv:1908.02040. Bibcode:2019A&A...630A.119M. doi:10.1051/0004-6361/201935885. S2CID 247759810.
  14. Herrero, A.; Kudritzki, R. P.; Vilchez, J. M.; Kunze, D.; Butler, K.; Haser, S. (1992). "Intrinsic parameters of galactic luminous OB stars". Astronomy and Astrophysics. 261: 209. Bibcode:1992A&A...261..209H.
  15. Sung, Hwankyung; Stauffer, John R.; Bessell, Michael S. (2009). "A Spitzer View of the Young Open Cluster NGC 2264". The Astronomical Journal. 138 (4): 1116–1136. arXiv:0906.3072. Bibcode:2009AJ....138.1116S. doi:10.1088/0004-6256/138/4/1116. S2CID 5272305.
  16. Bernacca, P. L.; Perinotto, M. (1970). "A catalogue of stellar rotational velocities". Contributi Osservatorio Astronomico di Padova in Asiago. 239 (1): 1. Bibcode:1970CoAsi.239....1B.
  17. Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (2010). "Masses and luminosities of O- and B-type stars and red supergiants". Astronomische Nachrichten. 331 (4): 349–360. arXiv:1003.2335. Bibcode:2010AN....331..349H. doi:10.1002/asna.200911355. S2CID 111387483.
  18. 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.
  19. 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.



На других языках

- [en] S Monocerotis

[es] S Monocerotis

S Monocerotis (S Mon / 15 Monocerotis / HD 47839 / HR 2456) es una estrella en la constelación de Monoceros, el unicornio, de magnitud aparente +4,66.[1] La distancia a la que se encuentra no es bien conocida; medidas directas de paralaje la sitúan a poco más de 1000 años luz de distancia del Sistema Solar pero si, como es probable, forma parte del cúmulo NGC 2264, su distancia sería considerablemente mayor, en torno a 2350 años luz.[2]

[ru] S Единорога

S Единорога (англ. S Monocerotis), также 15 Единорога — массивная кратная переменная звезда в созвездии Единорога. Ярчайшая звезда в скоплении Рождественская ёлка в области NGC 2264.


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