| luminosity = 1,820[13]
| temperature = 3,596[13]
| metal_fe = 0.00[14]
}}{{Starbox catalog
| names = 20 Librae, CD–24 11834, FK5 556, HD 133216, HIP 73714, HR 5603, SAO 183139.,[19] WDS 15041-2517[20]
}}{{Starbox reference
|Simbad=sig+Lib
}}{{Starbox end}}Sigma Librae (σ Librae, abbreviated Sig Lib, σ Lib) is a binary star[20] in the constellation of Libra. The apparent visual magnitude is +3.29,[5] making it visible to the naked eye. Based upon parallax measurements, this system is at a distance of roughly {{Convert|288|ly|pc|abbr=off|lk=on}} from the Sun, with a 2% margin of error.[1] At that distance, the visual magnitude is diminished by 0.20 ± 0.17 from extinction caused by intervening gas and dust.[14]The two components are designated Sigma Librae A (also named Brachium[1]) and B.
Nomenclature
σ Librae (Latinised to Sigma Librae) is the system's current Bayer designation (the star originally bore the designation γ Scorpii (Gamma Scorpii)[26] and did not receive its current designation until the new designation was agreed upon by Commission 3 of the International Astronomical Union (IAU) on July 31, 1930.[27]) The designations of the two components as Sigma Librae A and B derives from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[2]It bore the traditional Latin names Brachium (arm) and Cornu (horn), and the non-unique minor Arabic names Zuben el Genubi (southern claw) (shared with Alpha Librae); Zuben Hakrabi (shared with Gamma Librae and Eta Librae, also rendered as Zuban Alakrab), and Ankaa (shared with Alpha Phoenicis).{{citation needed|date=March 2017}} In 2016, the IAU organized a Working Group on Star Names (WGSN)[3] to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[4] It approved the name Brachium for the primary component Sigma Librae A on 5 September 2017. Ankaa had previously been approved as the name for Alpha Phoenicis on 29 July 2016. Both are now so included in the List of IAU-approved Star Names.[1]
In Chinese, {{lang|zh|折威}} ({{lang|zh-Latn|Shé Wēi}}), meaning Executions (asterism), refers to an asterism consisting of σ Librae, 50 Hydrae, 3 Librae, 4 Librae and 12 Librae.[5] Consequently, σ Librae are known as {{lang|zh|折威七}} ({{lang|zh-Latn|Shé Wēi qī}}, {{lang-en|the Seventh Star of Executions}}).[6]
Properties
The primary, Sigma Librae A, has a spectral class M2.5 III,[4] which places it in the red giant stage of its evolution. This is a semi-regular variable star with a single pulsation period of 20 days.[12] It shows small amplitude variations in magnitude of 0.10–0.15 on time scales as brief as 15–20 minutes, with cycles of repetition over intervals of 2.5–3.0 hours.[36] This form of variability indicates that the star is on the asymptotic giant branch and is generating energy through the nuclear fusion of hydrogen and helium along concentric shells surrounding an inert core of carbon and oxygen.[37]
The companion, Sigma Librae B, is of the 16th magnitude and over an arc minute away.[20]
References
1. ^1 {{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |accessdate=16 December 2017}}
2. ^{{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. }}
3. ^{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN)|accessdate=22 May 2016}}
4. ^{{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 |accessdate=2018-07-14}}
5. ^{{zh icon}} 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}}.
6. ^{{zh icon}} AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 28 日
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8. ^1 2 {{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|author1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}
9. ^1 2 3 4 5 6 {{citation | first=F. | last=van Leeuwen |date=November 2007 | title=Validation of the new Hipparcos reduction | journal=Astronomy and Astrophysics | volume=474 | issue=2 | pages=653–664 | bibcode=2007A&A...474..653V | doi=10.1051/0004-6361:20078357 | postscript=. |arxiv = 0708.1752 }}
10. ^1 {{citation | display-authors=1 | title=Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions | journal=Veröff. Astron. Rechen-Inst. Heidelb | volume=35 | last1=Wielen | first1=R. | last2=Schwan | first2=H. | last3=Dettbarn | first3=C. | last4=Lenhardt | first4=H. | last5=Jahreiß | first5=H. | last6=Jährling | first6=R. | publisher=Astronomisches Rechen-Institut Heidelberg | issue=35 | year=1999 | bibcode=1999VeARI..35....1W | postscript=. }}
11. ^1 2 3 {{citation | last1=Nicolet | first1=B. | year=1978 | title=Photoelectric photometric Catalogue of homogeneous measurements in the UBV System | journal=Astronomy and Astrophysics Supplement Series | volume=34 | pages=1–49 | bibcode=1978A&AS...34....1N | postscript=. }}
12. ^1 2 {{citation | last1=Yeşilyaprak | first1=C. | last2=Aslan | first2=Z. | title=Period-luminosity relation for M-type semiregular variables from Hipparcos parallaxes | journal=Monthly Notices of the Royal Astronomical Society | volume=355 | issue=2 | pages=601–607 |date=December 2004 | doi=10.1111/j.1365-2966.2004.08344.x | bibcode=2004MNRAS.355..601Y | postscript=. }}
13. ^1 {{citation | last1=Ruban | first1=E. V. | last2=Arkharov | first2=A. A. | title=Microvariability and fast variability of stars. II. The semiregular red giants L2 Pup, 2 Cen, η Gem, and σ Lib | journal=Astrophysics | volume=53 | issue=4 | pages=523–535 |date=December 2010 | doi=10.1007/s10511-010-9144-7 | bibcode=2010Ap.....53..523R | postscript=. }}
14. ^1 {{citation | title=sig Lib -- Semi-regular pulsating Star | work=SIMBAD | publisher=Centre de Données astronomiques de Strasbourg | url=http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Sigma+Librae | accessdate=2012-01-14 | postscript=. }}
15. ^1 {{citation | first1=Robert | last1=Burnham | title=Burnham's celestial handbook: an observer's guide to the universe beyond the Solar System | volume=2 | series=Dover Books on Astronomy | edition=2nd | publisher=Courier Dover Publications | year=1978 | isbn=0486235688 | page=1108 | url=https://books.google.com/books?id=wB9uZ9lH5bgC&pg=PA1108 | postscript=. }}
16. ^1 {{citation | title=Report of Commissions: Ephemerides | journal=Transactions of the International Astronomical Union | page=20 | volume=4 | year=1932 | url=https://books.google.com/books?id=3G03AAAAIAAJ&pg=PA20 | postscript=. }}
17. ^1 {{citation | last1=Lebzelter | first1=T. | last2=Hron | first2=J. | title=BRITE stars on the AGB | journal=Communications in Asteroseismology | volume=152 | pages=178–181 |date=January 2008 | doi=10.1553/cia152s178 | bibcode=2008CoAst.152..178L }}
18. ^1 2 3 {{citation | display-authors=1 | last1=Dehaes | first1=S. | last2=Bauwens | first2=E. | last3=Decin | first3=L. | last4=Eriksson | first4=K. | last5=Raskin | first5=G. | last6=Butler | first6=B. | last7=Dowell | first7=C. D. | last8=Ali | first8=B. | last9=Blommaert | first9=J. A. D. L. | title=Structure of the outer layers of cool standard stars | journal=Astronomy & Astrophysics | volume=533 | page=A107 |date=September 2011 | doi=10.1051/0004-6361/200912442 | bibcode=2011A&A...533A.107D |arxiv = 0905.1240 }}
19. ^1 2 {{cite journal|bibcode= 1989ApJS...71..245K |title= The Perkins catalog of revised MK types for the cooler stars |journal= Astrophysical Journal Supplement Series |volume= 71 |pages= 245 |author1= Keenan |first1= Philip C |last2= McNeil |first2= Raymond C |year= 1989 |doi= 10.1086/191373 }}
20. ^1 2 3 {{cite web | url=http://ad.usno.navy.mil/wds/ | title=Washington Double Star Catalog | publisher=United States Naval Observatory | accessdate=2 January 2018 | deadurl=yes | archiveurl=https://web.archive.org/web/20110214155533/http://ad.usno.navy.mil/wds/ | archivedate=14 February 2011 | df= }}