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Sigma Scorpii

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"Al Niyat" redirects here. For the other star that traditionally bore this name, seeTau Scorpii.
Sigma Scorpii
Location of σ Scorpii (circled)
Observation data
EpochJ2000.0EquinoxJ2000.0
Constellation Scorpius
Right ascension 16h21m11.31571s[1]
Declination −25° 35′ 34.0515″[1]
Apparent magnitude(V) +2.88[2]
Characteristics
Spectral type B1 III[3]+ B1 V[4]
U−Bcolor index −0.70[2]
B−Vcolor index +0.13[2]
Astrometry
Radial velocity(Rv)−0.4[5]km/s
Proper motion(μ)RA:−10.60[1]mas/yr
Dec.:−16.28[1]mas/yr
Distance568+75
−59ly
(174+23
−18[4]pc)
Absolute magnitude(MV)−4.12±0.34/−3.32±0.34[4]
Orbit[4]
Primaryσ Sco Aa1
Companionσ Sco Aa2
Period(P)33.010±0.002days
Semi-major axis(a)3.62±0.06mas
Eccentricity(e)0.3220±0.0012
Inclination(i)158.2±2.3°
Longitude of the node(Ω)104±5°
Periastronepoch(T)34889.0±1.0MJD
Argument of periastron(ω)
(secondary)		283±5°
Details
σ Sco Aa1
Mass18.4±5.4,[4]17.2-18.0[6]M☉
Radius12.7±1.8[4]R☉
Luminosity29,000±8,000,[4]95,500[6]L☉
Surface gravity(logg)3.85[4]cgs
Temperature26,150±1,070,[4]27,700[6]K
Metallicity[Fe/H]−0.20±0.20[7]dex
Rotational velocity(vsini)25[8]km/s
Age8.0±0.2,[9]8-10[6]Myr
σ Sco Aa2
Mass11.9±3.1[4]M☉
Radius11[4]R☉
Luminosity16000±4000[4]L☉
Other designations
Alniyat, Al Niyat, Pekehāwani, 20 Scorpii,ADS10009,CD-25 11485,FK5607,HD147165,HIP80112,HR6084,SAO184336,WDS16212-2536.[10]
Database references
SIMBADdata

Sigma Scorpii(orσ Scorpii,abbreviatedSigma Scoorσ Sco), is amultiple star systemin theconstellationofScorpius,located near the red supergiantAntares,which outshines it. This system has a combinedapparent visual magnitudeof +2.88,[2]making it one of thebrighter membersof the constellation. Based uponparallaxmeasurements made during theHipparcosmission, the distance to Sigma Scorpii is roughly 696light-years(214parsecs).[1]Northet al.(2007) computed a more accurate estimate of568+75
−59light years (174+23
−18parsecs).[4]

The system consists of aspectroscopic binarywith components designated Sigma Scorpii Aa1 (officially namedAlniyat/ælˈnaɪjæt/,the traditional name for the entire star system)[11][12]and aBeta Cephei variable) and Aa2; a third component (designated Sigma Scorpii Ab) at 0.4arcsecondsfrom the spectroscopic pair, and a fourth component (Sigma Scorpii B) at about 20 arcseconds.[13]

Nomenclature

[edit]
Rho Ophiuchi cloud complexin the infrared: the "red" at bottom right is 22-micron infrared light from Sigma Scorpii being reflected off the surrounding dust (Sh2-9).

σ Scorpii(LatinisedtoSigma Scorpii) is the star system'sBayer designation.The designations of the four components asSigma Scorpii Aa1,Aa2,AbandBderive from the convention used by the Washington Multiplicity Catalog (WMC) formultiple star systems,and adopted by theInternational Astronomical Union(IAU).[14]

Sigma Scorpii andTau Scorpiitogether bore the traditional nameAl Niyat(orAlniyat) derived from theArabicالنياطal-niyāţ"the arteries" and referring to their position flanking the starAntares,the scorpion's heart, with Sigma Scorpii just to the north.[15]

In 2016, theInternational Astronomical Unionorganized aWorking Group on Star Names(WGSN)[16]to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entiremultiple systems.[17]It approved the nameAlniyatfor the component Sigma Scorpii Aa1 on February 1, 2017 and it is now so included in the List of IAU-approved Star Names.[12]

InChinese,Tâm túc(Xīn Xiù), meaningHeart,refers to anasterismconsisting of Sigma Scorpii, Antares and Tau Scorpii.[18]Consequently, theChinese namefor Sigma Scorpii itself isTâm túc nhất(Xīn Xiù yī), "the First Star of Heart".[19]

The indigenousBoorongpeople of northwesternVictoriainAustraliasaw this star and Tau Scorpii as wives ofDjuit(Antares).[20]

Properties

[edit]
Alight curvefor Sigma Scorpii, plotted fromHipparcosdata[21]

The brightest component of the system, Sigma Scorpii Aa, is a double-linedspectroscopic binary,which means that the pair has not beenresolvedusing a telescope. Instead, theirorbitis determined by changes in their combinedspectrumcaused by theDoppler shift.This indicates that the pair complete an orbit every 33.01 days and have anorbital eccentricityof 0.32.[4]

The primary component of the spectroscopic binary, Sigma Scorpii Aa1, is anevolvedgiant starwith astellar classificationof B1 III.[3]It has around 18 times the massof the Sunand 12 times theSun's radius.[4]This star is radiating about29000times the luminosityof the Sunfrom itsouter envelopeat aneffective temperatureof26150K.[4]This is avariable starof theBeta Cephei type,causing the apparent magnitude to vary between +2.86 and +2.94 with multiple periods of0.2468429,0.239671,and 8.2 days. During each pulsation cycle, the temperature of the star varies by4000±2000 K.[4]The other member of the core pair, Sigma Scorpii Aa2, is amain sequencestar with a classification of B1 V.[4]

Orbiting this binary at a separation of half anarcsecond,or at least 120Astronomical units(AU), four times theSun–Neptunedistance, is the magnitude +5.2 Sigma Scorpii Ab, which has anorbital periodof over a hundred years. Even farther out at 20 arcseconds, or more than 4500 AU, is Sigma Scorpii B with a magnitude of +8.7. It isclassifiedas a B9dwarf.

Given its position, youth, and space velocity, the Sigma Scorpii system is a likely member of theGould Belt,[22]and in particular the Upper Scorpius subgroup of theScorpius–Centaurus association(Sco OB2). Recent isochronal age estimates for the system yield ages of 8–10 million years through comparison of theHR diagrampositions for the stars to modernevolutionary tracks.[4][6]This agrees well with the mean age for the Upper Scorpius group which is approximately 11 million years.[6]

References

[edit]
  1. ^abcdevan Leeuwen, F. (November 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.S2CID18759600.
  2. ^abcdJohnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars".Communications of the Lunar and Planetary Laboratory.4(99): 99.Bibcode:1966CoLPL...4...99J.
  3. ^abHouk, Nancy (1978),Michigan catalogue of two-dimensional spectral types for the HD stars,vol. 4, Ann Arbor: Dept. of Astronomy, University of Michigan,Bibcode:1988mcts.book.....H
  4. ^abcdefghijklmnopqrsNorth, J. R.; et al. (September 2007), "Orbital solution and fundamental parameters of σ Scorpii",Monthly Notices of the Royal Astronomical Society,380(3): 1276–1284,arXiv:0707.0897,Bibcode:2007MNRAS.380.1276N,doi:10.1111/j.1365-2966.2007.12188.x,S2CID14636283
  5. ^Wilson, R. E. (1953). "General Catalogue of Stellar Radial Velocities".Carnegie Institute Washington D.C. Publication.Carnegie Institute of Washington D.C.Bibcode:1953GCRV..C......0W.
  6. ^abcdefMark J. Pecaut; Eric E. Mamajek & Eric J. Bubar (February 2012). "A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius-Centaurus OB Association".Astrophysical Journal.746(2): 154.arXiv:1112.1695.Bibcode:2012ApJ...746..154P.doi:10.1088/0004-637X/746/2/154.S2CID118461108.
  7. ^Niemczura, E.; Daszyńska-Daszkiewicz, J. (April 2005), "Metallicities of the β Cephei stars from low-resolution ultraviolet spectra",Astronomy and Astrophysics,433(2): 659–669,arXiv:astro-ph/0410440,Bibcode:2005A&A...433..659N,doi:10.1051/0004-6361:20040396,S2CID14295631.Note: value taken from [m/H].
  8. ^Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars",The Astrophysical Journal,573(1): 359–365,Bibcode:2002ApJ...573..359A,doi:10.1086/340590
  9. ^Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun",Monthly Notices of the Royal Astronomical Society,410(1): 190–200,arXiv:1007.4883,Bibcode:2011MNRAS.410..190T,doi:10.1111/j.1365-2966.2010.17434.x,S2CID118629873
  10. ^"sig Sco".SIMBAD.Centre de données astronomiques de Strasbourg.
  11. ^Kunitzsch, Paul; Smart, Tim (2006).A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations(2nd rev. ed.). Cambridge, Massachusetts: Sky Pub.ISBN978-1-931559-44-7.
  12. ^ab"Naming Stars".IAU.org.Retrieved16 December2017.
  13. ^"Washington Double Star Catalog".United States Naval Observatory. Archived fromthe originalon 14 February 2011.Retrieved2 January2018.
  14. ^Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets".arXiv:1012.0707[astro-ph.SR].
  15. ^Allen, Richard Hinckley(1963) [1899].Star Names: Their Lore and Meaning(Reprinted.).New York,NY:Dover PublicationsInc. p. 371.ISBN0-486-21079-0.
  16. ^"International Astronomical Union | IAU".www.iau.org.Retrieved2017-03-31.
  17. ^"WG Triennial Report (2015-2018) - Star Names"(PDF).p. 5.Retrieved2018-07-14.
  18. ^(in Chinese)Trung quốc tinh tọa thần thoại,written by trần cửu kim. Published by đài loan thư phòng xuất bản hữu hạn công tư, 2005,ISBN978-986-7332-25-7.
  19. ^(in Chinese)Hương cảng thái không quán - nghiên cứu tư nguyên - lượng tinh trung anh đối chiếu biểuArchived2008-10-25 at theWayback Machine,Hong Kong Space Museum. Accessed on line November 23, 2010.
  20. ^Hamacher, Duane W.; Frew, David J. (2010). "An Aboriginal Australian Record of the Great Eruption of Eta Carinae".Journal of Astronomical History & Heritage.13(3): 220–34.arXiv:1010.4610.Bibcode:2010JAHH...13..220H.doi:10.3724/SP.J.1440-2807.2010.03.06.S2CID118454721.
  21. ^"Light Curve".Hipparcos ESA.ESA.Retrieved17 February2022.
  22. ^Bobylev, V. V.; Bajkova, A. T. (September 2007), "Kinematics of the Scorpius-Centaurus OB association",Astronomy Letters,33(9): 571–583,arXiv:0708.0943,Bibcode:2007AstL...33..571B,doi:10.1134/S1063773707090010,S2CID15785349
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