S Monocerotis

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Template:Short description

S Monocerotis
File:Monoceros constellation map.svg
S Monocerotis lies in NGC 2264 at the very northern edge of Monoceros.
Observation data
Epoch J2000      Equinox J2000
Constellation Monoceros
A
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) 4.66[2] (4.62 - 4.68[3]) + 5.90[2]
B
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) 7.830[1]
Characteristics
Spectral type O7V((f))zvar[4] + O9.5Vn[5] + B2V[6]
U−B Template:Engvar −1.034[7]
B−V Template:Engvar −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]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd 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]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Orbit[13]
PrimaryAa
CompanionAb
Period (P)Script error: No such module "val". yr
Semi-major axis (a)Script error: No such module "val".
Eccentricity (e)Script error: No such module "val".
Inclination (i)Script error: No such module "val".°
Longitude of the node (Ω)Script error: No such module "val".°
Periastron epoch (T)B Script error: No such module "val".
Argument of periastron (ω)
(secondary)		Script error: No such module "val".°
Details
Aa
Mass29.1[2] Template:Solar mass
Radius9.9[14] Template:Solar radius
Luminosity214,000[14] Template:Solar luminosity
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] Template:Solar mass
Metallicity [Fe/H]{{{metal_fe2}}} dex
Age3.1[17] Myr
Other designations
15 Monocerotis, HD 47839, HIP 31978, HR 2456, SAO 114258, BD+10°1220
Database references
SIMBADdata
ARICNSdata

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File:NGC 2264 cluster.jpg
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, 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 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 Template:Solar mass. 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 Template:Solar mass and Template:Solar mass.[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 Script error: No such module "val". and Script error: No such module "val". respectively, consistent with the expected distance to the cluster.

References

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  9. ↑ a b c d Script error: No such module "Citation/CS1".
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  11. ↑ a b c Template:Cite Gaia EDR3
  12. ↑ a b c Template:Cite Gaia EDR3
  13. ↑ a b Script error: No such module "Citation/CS1".
  14. ↑ a b c Script error: No such module "Citation/CS1".
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  17. ↑ Script error: No such module "Citation/CS1".
  18. ↑ Script error: No such module "Citation/CS1".
  19. ↑ Script error: No such module "Citation/CS1".

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External links

Template:Stars of Monoceros Script error: No such module "Navbox".

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