S Monocerotis

{{Short description|Star in the constellation Monoceros}}

{{Starbox begin

| name=S Monocerotis

}}

{{Starbox image

| image=300px

| caption=S Monocerotis lies in NGC 2264 at the very northern edge of Monoceros.

}}

{{Starbox observe 2s

| epoch=J2000

| constell=Monoceros

| component1=A

| ra1={{RA|06|40|58.656}}{{cite journal|bibcode=2000A&A...355L..27H|title=The Tycho-2 catalogue of the 2.5 million brightest stars|journal=Astronomy and Astrophysics|volume=355|pages=L27|last1=Høg|first1=E.|last2=Fabricius|first2=C.|last3=Makarov|first3=V. V.|last4=Urban|first4=S.|last5=Corbin|first5=T.|last6=Wycoff|first6=G.|last7=Bastian|first7=U.|last8=Schwekendiek|first8=P.|last9=Wicenec|first9=A.|year=2000|doi=10.1888/0333750888/2862|isbn=0333750888}}

| dec1={{DEC|+09|53|44.71}}

| appmag_v1=4.66 {{nowrap|(4.62 - 4.68)}} + 5.90

| component2=B

| ra2={{RA|06|40|58.566}}

| dec2={{DEC|+09|53|42.20}}

| appmag_v2=7.830

}}

{{Starbox character

| class=O7V((f))zvar{{cite journal|bibcode= 2011ApJS..193...24S|title= The Galactic O-Star Spectroscopic Survey. I. Classification System and Bright Northern Stars in the Blue-violet at R ~ 2500|journal= The Astrophysical Journal Supplement|volume= 193|issue= 2|pages= 24|last1= Sota|first1= A.|last2= Maíz Apellániz|first2= J.|last3= Walborn|first3= N. R.|last4= Alfaro|first4= E. J.|last5= Barbá|first5= R. H.|last6= Morrell|first6= N. I.|author-link6=Nidia Morrell |last7= Gamen|first7= R. C.|last8= Arias|first8= J. I.|year= 2011|doi= 10.1088/0067-0049/193/2/24|arxiv = 1101.4002 |s2cid= 119248206}} + O9.5Vn{{cite journal|bibcode=2010NewA...15..302C|title=A new orbit of binary 15 Monocerotis|journal=New Astronomy|volume=15|issue=3|pages=302–306|last1=Cvetković|first1=Z.|last2=Vince|first2=I.|last3=Ninković|first3=S.|year=2010|doi=10.1016/j.newast.2009.09.002}} + B2V

| b-v=−0.261

| u-b=−1.034

| variable=Ia{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}

}}

{{Starbox astrometry

| component1 = A

| radial_v=22.00

| prop_mo_ra=−2.61

| prop_mo_dec=−1.61

| parallax=3.55

| p_error=0.50

| parallax_footnote=

| dist_pc=720

| absmag_v=−5.21{{cite journal|bibcode=1986A&A...159..223F|title=Of-stars in young open clusters|journal=Astronomy and Astrophysics|volume=159|pages=223|last1=Feinstein|first1=A.|last2=Vazquez|first2=R. A.|last3=Benvenuto|first3=O. G.|year=1986}}

}}

{{Starbox astrometry|no_heading=y

| component1 = B

| prop_mo_ra = −1.971

| prop_mo_dec = −4.225

| parallax = 1.4019

| p_error = 0.0984

| parallax_footnote =

| component2 = C

| prop_mo_ra2 = −1.464

| prop_mo_dec2 = −2.746

| parallax2 = 1.5438

| p_error2 = 0.0394

| parallax_footnote2 =

}}

{{Starbox orbit

| reference =

| primary = Aa

| name = Ab

| period = {{val|108|12}}

| axis =

| axis_unitless = {{val|112.5|6|ul=mas}}

| eccentricity = {{val|0.770|0.023|0.030}}

| inclination = {{val|47|2}}

| node = {{val|60|3}}

| periastron = B {{val|1996.05|0.15|0.10}}

| periarg = {{val|63|4}}

}}

{{Starbox detail

| component1=Aa

| mass=29.1

| radius=9.9{{cite journal|bibcode=1992A&A...261..209H|title=Intrinsic parameters of galactic luminous OB stars|journal=Astronomy and Astrophysics|volume=261|pages=209|last1=Herrero|first1=A.|last2=Kudritzki|first2=R. P.|last3=Vilchez|first3=J. M.|last4=Kunze|first4=D.|last5=Butler|first5=K.|last6=Haser|first6=S.|year=1992}}

| luminosity=214,000

| temperature=38,500

| metal_fe=

| rotation=

| rotational_velocity=120

| gravity=4.5{{cite journal|bibcode=2009AJ....138.1116S|title=A Spitzer View of the Young Open Cluster NGC 2264|journal=The Astronomical Journal|volume=138|issue=4|pages=1116–1136|last1=Sung|first1=Hwankyung|last2=Stauffer|first2=John R.|last3=Bessell|first3=Michael S.|year=2009|doi=10.1088/0004-6256/138/4/1116|arxiv = 0906.3072 |s2cid=5272305}}

| component2=Ab

| mass2=21.3

| radius2=

| luminosity2=

| temperature2=

| metal2=

| rotation2=

| rotational_velocity2=

| gravity2=

| age_myr2=3.1{{cite journal|bibcode= 2010AN....331..349H|title= Masses and luminosities of O- and B-type stars and red supergiants|journal= Astronomische Nachrichten|volume= 331|issue= 4|pages= 349–360|last1= Hohle|first1= M. M.|last2= Neuhäuser|first2= R.|last3= Schutz|first3= B. F.|year= 2010|doi= 10.1002/asna.200911355|arxiv = 1003.2335 |s2cid= 111387483}}

}}

{{Starbox catalog

| names=15 Monocerotis, HD 47839, HIP 31978, HR 2456, SAO 114258, BD+10°1220

}}

{{Starbox reference

| Simbad=HD+47839

| ARICNS=00151

}}

{{Starbox end}}

File:NGC 2264 cluster.jpg 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.{{Cite journal | last1 = Worley | first1 = C. E. | last2 = Douglass | first2 = G. G. | doi = 10.1051/aas:1997239 | title = The Washington Double Star Catalog (WDS, 1996.0) | journal = Astronomy and Astrophysics Supplement Series | volume = 125 | issue = 3 | pages = 523 | year = 1997 |bibcode = 1997A&AS..125..523W | doi-access = free }} 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 {{solar mass|7.31|link=y}}. Designated component C is an 11th-magnitude B8V star. 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. Since 1943, the spectrum of this star has served as the MK standard for O7 by which other stars are classified. 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 {{solar mass|31}} and {{solar mass|11}}.

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. Gaia Early Data Release 3 contains parallaxes for the companions components B and C of {{val|1.4|ul=mas}} and {{val|1.5|u=mas}} respectively, consistent with the expected distance to the cluster.

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