sigma Librae
{{short description|Star in the constellation Libra}}
{{Starbox begin
| name = σ Librae
}}
{{Starbox image
| image=
{{Location mark
|image=Libra constellation map.svg|alt=|float=center|width=260
|label=|position=right
|mark=Red circle.svg|mark_width=10|mark_link=σ Lib
|x=556|y=698
}}
|caption=Location of σ Librae (circled)
}}
{{Starbox observe
| epoch = J2000.0
| constell = Libra
| dec = {{DEC|-25|16|55.0905}}
}}
{{Starbox character
| r-i =
| variable = SRb
}}
{{Starbox astrometry
| prop_mo_ra = {{val|-73.484}}
| prop_mo_dec = {{val|-42.632}}
| parallax = 12.539
| p_error = 0.3
| dist_pc = {{val|80.02|1.61|1.92}}
| dist_ly = {{val|{{convert|80.02|pc|ly|disp=number|sigfig=4}}|{{convert|1.61|pc|ly|disp=number|sigfig=3}}|{{convert|1.92|pc|ly|disp=number|sigfig=3}}}}
}}
{{Starbox detail
| luminosity = 1,800{{efn|1=Luminosity calculated from Sigma Librae's absolute bolometric magnitude, with respect to the Sun's absolute bolometric magnitude of 4.74:
10{{sup|0.4{{bull}}(4.74−(−3.4))}} ≈ {{solar luminosity|1,800|link=y}}.}}
}}
{{Starbox catalog
| names = Brachium, 20 Librae, CD−24 11834, FK5 556, HD 133216, HIP 73714, HR 5603, SAO 183139., WDS 15041-2517
}}
{{Starbox reference
|Simbad=sig+Lib
}}
{{Starbox end}}
Sigma Librae (σ Librae, abbreviated Sigma Lib, σ Lib) is a binary star in the constellation of Libra. The apparent visual magnitude is +3.29, making it visible to the naked eye. Based upon parallax measurements, this system is at a distance of roughly {{Convert|260|ly|pc|abbr=off|lk=on}} from the Sun, with a 2% margin of error. At that distance, the visual magnitude is diminished by {{val|0.20|0.17}} from extinction caused by intervening gas and dust.
The two components are designated Sigma Librae A (officially named Brachium {{IPAc-en|'|b|r|ei|k|i|@|m}},{{OED|brachium}} the traditional name for the system){{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |accessdate=16 December 2017}} and B.
Nomenclature
σ Librae (Latinised to Sigma Librae) is the system's current Bayer designation (the star originally bore the designation Gamma Scorpii 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.) 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).{{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.}}
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){{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}} to catalog and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.{{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}} 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.
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.{{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}}. Consequently, the Chinese name for σ Librae is {{lang|zh|折威七}} ({{lang|zh-Latn|Shé Wēi qī}}, {{langx|en|the Seventh Star of Executions}}).{{in lang|zh}} [http://aeea.nmns.edu.tw/2006/0606/ap060628.html AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 6 月 28 日] {{Webarchive|url=https://web.archive.org/web/20110716122210/http://aeea.nmns.edu.tw/2006/0606/ap060628.html |date=2011-07-16 }}
Properties
File:SigmaLibLightCurve.png for Sigma Librae, plotted from Hipparcos data]]
The primary, Sigma Librae A, has a spectral class M2.5 III, 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. 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. 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 within concentric shells surrounding an inert core of carbon and oxygen.
The companion, Sigma Librae B, is of the 16th magnitude and over an arc minute away.
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Notes
{{Notelist}}
References
{{reflist|refs=
| title=The HIPPARCOS and TYCHO catalogues | author=EAS
| journal=Astrometric and Photometric Star Catalogues Derived from the ESA Hipparcos Space Astrometry Mission
| publication-place=Noordwijk, Netherlands | publisher=ESA Publications Division
| year=1997 | series=ESA SP Series | volume=1200 | isbn=9290923997
| bibcode=1997HIP...C......0E
| url=https://cdsarc.cds.unistra.fr/viz-bin/ftp-index?/ftp/cats/more/HIP/cdroms/cats
| access-date=15 October 2022}}
{{Cite DR3|6227443304915069056}}
{{cite constellation|HR 5603}}
{{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=. | doi-access=free}}
}}
External links
- {{citation | first1=James B. | last1=Kaler | work=Stars | title=ZUBENHAKRABI (Sigma Librae = Gamma Scorpii) | publisher=University of Illinois | url=http://stars.astro.illinois.edu/sow/zubenh.html | accessdate=2012-03-22 }}
{{Stars of Libra}}
{{DEFAULTSORT:Sigma Librae}}
Category:Libra (constellation)