{{redirect|Al Niyat|the other star that traditionally bore this name|Tau Scorpii}} {{short description|Multiple star system in the constellation of Scorpius}} {{Starbox begin | name = Sigma Scorpii }} {{Starbox image | image = {{Location mark |image=Scorpius IAU.svg|alt=|float=center|width=260 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link= |x=600|y=545 }} | caption=Location of σ Scorpii (circled) }} {{Starbox observe | epoch = J2000.0 | ra = {{RA|16|21|11.31571}}<ref name=aaa474_2_653/> | dec = {{DEC|-25|35|34.0515}}<ref name=aaa474_2_653/> | appmag_v = +2.88<ref name=clpl4/> | constell = Scorpius }} {{Starbox character | class = B1 III<ref name=houk1978/> + B1 V<ref name=mnras380_3_1276/> | b-v = +0.13<ref name=clpl4/> | u-b = −0.70<ref name=clpl4/> | variable = }} {{Starbox astrometry | radial_v = −0.4<ref name=gcsrv/> | prop_mo_ra = −10.60<ref name=aaa474_2_653/> | prop_mo_dec = −16.28<ref name=aaa474_2_653/> | dist_ly = {{val|568|+75|-59}} | dist_pc = {{val|174|+23|-18}}<ref name=mnras380_3_1276/> | absmag_v = {{val|-4.12|0.34}} / {{val|-3.32|0.34}}<ref name=mnras380_3_1276/> }} {{Starbox orbit | reference = <ref name=mnras380_3_1276/> | primary = σ Sco Aa1 | name = σ Sco Aa2 | period = <!--Period (in years)--> | period_unitless = {{val|33.010|0.002}} days | axis = <!--Semimajor axis (in arcseconds)--> | axis_unitless = {{val|3.62|0.06}} mas | eccentricity = {{val|0.3220|0.0012}} | inclination = {{val|158.2|2.3}} | node = {{val|104|5}} | periastron = {{val|34889.0|1.0}} MJD | periarg = {{val|283|5}} }} {{Starbox detail | component1 = σ Sco Aa1 | mass = {{val|18.4|5.4}},<ref name=mnras380_3_1276/> {{nowrap|17.2-18.0}}<ref name=Pecaut/> | radius = {{val|12.7|1.8}}<ref name=mnras380_3_1276/> | gravity = 3.85<ref name=mnras380_3_1276/> | metal_fe = {{val|-0.20|0.20}}<ref name=aaa433_2_659/> | age_myr = {{val|8.0|0.2}},<ref name=mnras410_1_190/> {{nowrap|8-10}}<ref name=Pecaut/> | luminosity = {{val|29,000|8,000|fmt=commas}},<ref name=mnras380_3_1276/> 95,500<ref name=Pecaut/> | temperature = {{val|26150|1070|fmt=commas}},<ref name=mnras380_3_1276/> 27,700<ref name=Pecaut/> | rotational_velocity = 25<ref name=apj573_1_359/> | component2 = σ Sco Aa2 | mass2 = {{val|11.9|3.1}}<ref name=mnras380_3_1276/> | radius2 = 11<ref name=mnras380_3_1276/> | luminosity2 = {{val|16,000|4,000}}<ref name=mnras380_3_1276/> }} {{Starbox catalog | names = Alniyat, Al Niyat, 20 Scorpii, ADS 10009, CD−25 11485, FK5 607, HD 147165, HIP 80112, HR 6084, SAO 184336, WDS 16212-2536.<ref name=SIMBAD/> }} {{Starbox reference |Simbad=sig+Sco }} {{Starbox end}}
'''Sigma Scorpii''' (or '''σ Scorpii''', abbreviated '''Sigma Sco''' or '''σ Sco'''), is a multiple star system in the constellation of Scorpius, located near the red supergiant Antares, which outshines it. This system has a combined apparent visual magnitude of +2.88,<ref name=clpl4/> making it one of the brighter members of the constellation. Based upon parallax measurements made during the Hipparcos mission, the distance to Sigma Scorpii is roughly 696 light-years (214 parsecs).<ref name=aaa474_2_653/> North ''et al.'' (2007) computed a more accurate estimate of {{val|568|+75|-59}} light years ({{val|174|+23|-18}} parsecs).<ref name=mnras380_3_1276/>
The system consists of a spectroscopic binary with components designated Sigma Scorpii Aa1 (officially named '''Alniyat''' {{IPAc-en|æ|l|'|n|ai|j|æ|t}}, the traditional name for the entire star system)<ref name=Kunitzsch/><ref name="IAU-LSN"/> and a Beta Cephei variable) and Aa2; a third component (designated Sigma Scorpii Ab) at 0.4 arcseconds from the spectroscopic pair, and a fourth component (Sigma Scorpii B) at about 20 arcseconds.<ref name="WDS"/>
== Nomenclature == [[File:Rho Ophiuchi.jpg|thumb|left|Rho Ophiuchi cloud complex in 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'' (Latinised to ''Sigma Scorpii'') is the star system's Bayer designation. The designations of the four components as ''Sigma Scorpii Aa1'', ''Aa2'', ''Ab'' and ''B'' derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).<ref name="planetnaming"/>
Sigma Scorpii and Tau Scorpii together bore the traditional name ''Al Niyat'' (or ''Alniyat'') derived from the Arabic النياط ''al-niyāţ'' "the arteries" and referring to their position flanking the star Antares, the scorpion's heart, with Sigma Scorpii just to the north.<ref name="allen1963"/>
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)<ref name=IAU/> to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.<ref name="TriRpt18"/> It approved the name ''Alniyat'' for the component Sigma Scorpii Aa1 on February 1, 2017 and it is now so included in the List of IAU-approved Star Names.<ref name="IAU-LSN"/>
In Chinese, {{lang|zh|心宿}} ({{lang|zh-Latn|Xīn Xiù}}), meaning ''Heart'', refers to an asterism consisting of Sigma Scorpii, Antares and Tau Scorpii.<ref name=zh/> Consequently, the Chinese name for Sigma Scorpii itself is {{lang|zh|心宿一}} ({{lang|zh-Latn|Xīn Xiù yī}}), "the First Star of Heart".<ref name=chinengstars/>
The indigenous Boorong people of northwestern Victoria in Australia saw this star and Tau Scorpii as wives of ''Djuit'' (Antares).<ref name=hamacher/>
The Hawaiian name of this star is Au-haele; it forms a line of three stars with Hōkū-‘ula (Antares) and Paikauhale (τ Scorpii).<ref name="IAU-CSN-new"/>
== Properties == [[File:SigmaScoLightCurve.png|thumb|left|A light curve for Sigma Scorpii, plotted from ''Hipparcos'' data<ref name=HIPCurve/>]] The brightest component of the system, Sigma Scorpii Aa, is a double-lined spectroscopic binary, which means that the pair has not been resolved using a telescope. Instead, their orbit is determined by changes in their combined spectrum caused by the Doppler shift. This indicates that the pair complete an orbit every 33.01 days and have an orbital eccentricity of 0.32.<ref name=mnras380_3_1276/>
The primary component of the spectroscopic binary, Sigma Scorpii Aa1, is an evolved giant star with a stellar classification of B1 III.<ref name=houk1978/> It has around 18 times the mass of the Sun and 12 times the Sun's radius.<ref name=mnras380_3_1276/> This star is radiating about {{val|29000}} times the luminosity of the Sun from its outer envelope at an effective temperature of {{val|26150|u=K}}.<ref name=mnras380_3_1276/> This is a variable star of the Beta Cephei type, causing the apparent magnitude to vary between +2.86 and +2.94 with multiple periods of {{val|0.2468429}}, {{val|0.239671}}, and 8.2 days. During each pulsation cycle, the temperature of the star varies by {{val|4000|2000|u=K}}.<ref name=mnras380_3_1276/> The other member of the core pair, Sigma Scorpii Aa2, is a main sequence star with a classification of B1 V.<ref name=mnras380_3_1276/>
Orbiting this binary at a separation of half an arcsecond, or at least 120 Astronomical units (AU), four times the Sun–Neptune distance, is the magnitude +5.2 Sigma Scorpii Ab, which has an orbital period of 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 is classified as a B9 dwarf.
Given its position, youth, and space velocity, the Sigma Scorpii system is a likely member of the Gould Belt,<ref name=al33_9_571/> and in particular the Upper Scorpius subgroup of the Scorpius–Centaurus association (Sco OB2). Recent isochronal age estimates for the system yield ages of 8–10 million years through comparison of the HR diagram positions for the stars to modern evolutionary tracks.<ref name=mnras380_3_1276/><ref name="Pecaut">{{Cite journal|author=Mark J. Pecaut|author2=Eric E. Mamajek|author3=Eric J. Bubar|name-list-style=amp|date=February 2012|title=A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius-Centaurus OB Association|journal=Astrophysical Journal|volume=746|issue=2|pages=154|arxiv = 1112.1695 |bibcode = 2012ApJ...746..154P |doi = 10.1088/0004-637X/746/2/154 |s2cid=118461108}}</ref> This agrees well with the mean age for the Upper Scorpius group which is approximately 11 million years.<ref name=Pecaut />
==References== <references> <ref name=hamacher>{{cite journal|author=Hamacher, Duane W.|author2=Frew, David J. |date=2010|title= An Aboriginal Australian Record of the Great Eruption of Eta Carinae|journal=Journal of Astronomical History & Heritage |volume=13|issue=3|pages= 220–34|doi=10.3724/SP.J.1440-2807.2010.03.06 |arxiv = 1010.4610 |bibcode = 2010JAHH...13..220H |s2cid=118454721 }}</ref>
<ref name=chinengstars>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_ala_alz.htm 香港太空館 - 研究資源 - 亮星中英對照表] {{webarchive|url=https://web.archive.org/web/20081025110153/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_ala_alz.htm |date=2008-10-25 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref>
<ref name=zh>{{in lang|zh}} ''中國星座神話'', written by 陳久金. Published by 台灣書房出版有限公司, 2005, {{ISBN|978-986-7332-25-7}}.</ref>
<ref name="TriRpt18">{{cite web | url=https://www.iau.org/static/science/scientific_bodies/working_groups/280/wg-starnames-triennial-report-2015-2018.pdf | page=5 | title=WG Triennial Report (2015-2018) - Star Names |access-date=2018-07-14}}</ref>
<ref name=IAU>{{Cite web|url=https://www.iau.org/science/scientific_bodies/working_groups/280/|title=International Astronomical Union {{!}} IAU|website=www.iau.org|access-date=2017-03-31}}</ref>
<ref name="allen1963">{{cite book | author=Allen, Richard Hinckley | author-link=Richard Hinckley Allen | date=1963 |orig-year=1899 | title=Star Names: Their Lore and Meaning | page=371 | edition=Reprint | publisher=Dover Publications Inc. | location=New York, NY | url= https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/home.html | isbn=0-486-21079-0 }}</ref>
<ref name="planetnaming">{{cite arXiv |title=On the naming convention used for multiple star systems and extrasolar planets |date=2010 |eprint=1012.0707 |class=astro-ph.SR |last1= Hessman |first1=F. V. |last2= Dhillon |first2=V. S. |last3= Winget |first3=D. E. |last4= Schreiber |first4=M. R. |last5= Horne |first5=K. |last6= Marsh |first6=T. R. |last7= Guenther |first7=E. |last8= Schwope |first8=A. |last9= Heber |first9=U. }}</ref>
<ref name="WDS">{{cite web | url=http://ad.usno.navy.mil/wds/ | title=Washington Double Star Catalog | publisher=United States Naval Observatory | access-date=2 January 2018 | url-status=dead | archive-url=https://web.archive.org/web/20110214155533/http://ad.usno.navy.mil/wds/ | archive-date=14 February 2011 }}</ref>
<ref name="IAU-LSN">{{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |access-date=16 December 2017}}</ref>
<ref name=Kunitzsch>{{cite book |last1=Kunitzsch |first1=Paul |last2=Smart |first2=Tim |date = 2006 |edition = 2nd rev. |title = A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations |publisher = Sky Pub |location = Cambridge, Massachusetts |isbn = 978-1-931559-44-7 }}</ref>
<ref name=HIPCurve>{{cite web |title=Light Curve |url=https://www.cosmos.esa.int/web/hipparcos/java-tools/light-curve |website=Hipparcos ESA |publisher=ESA |access-date=17 February 2022}}</ref>
<ref name=aaa474_2_653>{{cite journal | title=Validation of the new Hipparcos reduction | last=van Leeuwen | first=F. | journal=Astronomy and Astrophysics | volume=474 | issue=2 |date=November 2007 | pages=653–664 | doi=10.1051/0004-6361:20078357 | bibcode=2007A&A...474..653V |arxiv = 0708.1752 | s2cid=18759600 }}</ref>
<ref name=houk1978>{{cite book | last1=Houk | first1=Nancy | title=Michigan catalogue of two-dimensional spectral types for the HD stars | volume=4 | location=Ann Arbor | publisher=Dept. of Astronomy, University of Michigan | date=1978 | bibcode=1988mcts.book.....H }}</ref>
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<ref name=clpl4>{{cite journal | display-authors=1 | last1=Johnson | first1=H. L. | last2=Iriarte | first2=B. | last3=Mitchell | first3=R. I. | last4=Wisniewskj | first4=W. Z. | title=UBVRIJKL photometry of the bright stars | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | issue=99 | date=1966 | page=99 | bibcode=1966CoLPL...4...99J }}</ref>
<ref name=mnras410_1_190>{{cite journal | last1=Tetzlaff | first1=N. | last2=Neuhäuser | first2=R. | last3=Hohle | first3=M. M. | title=A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun | journal=Monthly Notices of the Royal Astronomical Society | volume=410 | issue=1 | pages=190–200 |date=January 2011 | doi=10.1111/j.1365-2966.2010.17434.x | doi-access=free | bibcode=2011MNRAS.410..190T |arxiv = 1007.4883 | s2cid=118629873 }}</ref>
<ref name=SIMBAD>{{cite simbad | title=sig Sco | access-date=}}</ref>
<ref name=mnras380_3_1276>{{cite journal | display-authors=1 | last1=North | first1=J. R. | last2=Davis | first2=J. | last3=Tuthill | first3=P. G. | last4=Tango | first4=W. J. | last5=Robertson | first5=J. G. | title=Orbital solution and fundamental parameters of σ Scorpii | journal=Monthly Notices of the Royal Astronomical Society | volume=380 | issue=3 | pages=1276–1284 |date=September 2007 | doi=10.1111/j.1365-2966.2007.12188.x | doi-access=free | bibcode=2007MNRAS.380.1276N |arxiv = 0707.0897 | s2cid=14636283 }}</ref>
<ref name=al33_9_571>{{cite journal | last1=Bobylev | first1=V. V. | last2=Bajkova | first2=A. T. | title=Kinematics of the Scorpius-Centaurus OB association | journal=Astronomy Letters | volume=33 | issue=9 | pages=571–583 |date=September 2007 | doi=10.1134/S1063773707090010 | bibcode=2007AstL...33..571B |arxiv = 0708.0943 | s2cid=15785349 }}</ref>
<ref name=aaa433_2_659>{{cite journal | last1=Niemczura | first1=E. | last2=Daszyńska-Daszkiewicz | first2=J. | title=Metallicities of the β Cephei stars from low-resolution ultraviolet spectra | journal=Astronomy and Astrophysics | volume=433 | issue=2 | pages=659–669 |date=April 2005 | doi=10.1051/0004-6361:20040396 | bibcode=2005A&A...433..659N |arxiv = astro-ph/0410440 | s2cid=14295631 }}. Note: value taken from [m/H].</ref>
<ref name="IAU-CSN-new">{{cite web |title=IAU Catalog of Star Names |url=https://exopla.net/star-names/modern-iau-star-names/ |access-date=14 May 2025}}</ref> </references>
{{Stars of Scorpius}}
Category:Scorpius Scorpii, Sigma Scorpii, 20 Category:Beta Cephei variables Category:B-type giants Category:B-type main-sequence stars 4 Alniyat Category:Upper Scorpius 080112 147165 CD-25 11485 6084