Alpha Librae

{{short description|Quadruple star in the constellation Libra}} {{Starbox begin | name = α Librae }} {{Starbox image | image= {{Location mark |image=Libra constellation map.svg|alt=|float=center|width=280 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=α Librae |x=657|y=410 }} |caption=Location of α Librae (circled) }} {{Starbox observe 2s | epoch = [[J2000.0]] | constell = [[Libra (constellation)|Libra]] | component1 = {{nobr|α¹ Lib}} {{nobr|(α Lib B)}} | ra1 = {{RA|14|50|41.18097}}<ref name=hipparcos/> | dec1 = {{DEC|-15|59|50.0482}}<ref name=hipparcos/> | appmag_v1 = +5.153<ref name=sps1966/> | component2 = {{nobr|α² Lib}} {{nobr|(α Lib A)}} | ra2 = {{RA|14|50|52.71309}}<ref name=hipparcos/> | dec2 = {{DEC|-16|02|30.3955}}<ref name=hipparcos/> | appmag_v2 = +2.741<ref name=sps1966/> }} {{Starbox character | component = α¹ Lib | class = F3 V<ref name=mk/> + M0{{endash}}1 V<ref name=Caballero2010/> | b-v = +0.39<ref name=EgUBV/> | u-b = −0.02<ref name=EgUBV/> | variable = }} {{Starbox character|no_heading=y | component = α² Lib | type = [[Main sequence]]<ref name=Zorec2012/><ref name=Takeda2018/> or [[blue straggler]] (α²&nbsp;A)<ref name=Waisberg2023/> | class = kA2hA5mA4 IV-V<ref name=Gray2006/> | b-v = +0.15<ref name=EgUBV/> | u-b = +0.10<ref name=EgUBV/> | variable = }} {{Starbox astrometry | component1 = α¹ Lib | radial_v = {{Val|−23.8|0.3}}<ref name=Fuhrmann2014/> | prop_mo_ra = −136.27<ref name=hipparcos/> | prop_mo_dec = −59.04<ref name=hipparcos/> | parallax = 43.52 | p_error = 0.43 | parallax_footnote = <ref name=hipparcos/> | absmag_v = +3.35<ref name=Holmerg2009/> | component2 = α² Lib | radial_v2 = | prop_mo_ra2 = −105.68<ref name=hipparcos/> | prop_mo_dec2 = −68.40<ref name=hipparcos/> | parallax2 = 43.03 | p_error2 = 0.19 | parallax_footnote2 = <ref name=hipparcos/> | absmag_v2 = +0.88<ref name=ap1999/> }} {{Starbox orbit | reference = <ref name=soar2023/> | primary = α¹ Lib A | name = α¹ Lib B | period = {{val|16.229|0.043}} | periastron = {{val|2021.95|0.12}} | eccentricity = {{val|0.244|0.008}} | axis = {{val|0.346|0.006}} | node = {{val|122.7|1.4}} | periarg = {{val|184.1|3.3}} | inclination = {{val|54.4|1.5}} | k1 = {{val|3.83|0.12}} }} {{Starbox orbit | reference = <ref name=Fuhrmann2014/> | primary = α² Lib A | name = α² Lib B | period_unitless = {{val|70.34|0.07}} days | axis_unitless= 0.52<ref name=Waisberg2023/> au | eccentricity = {{val|0.41|0.02}} | inclination = {{val|71|3}}<ref name=Waisberg2023/> | node = {{val|333|17}}<ref name=Waisberg2023/> | periastron = JD {{val|2455294.3|0.5}} | periarg = {{val|48|7}} | k2 = {{val|43.1|0.5}} }} {{Starbox detail | component1 = α² Lib A | mass = 1.95<ref name=Waisberg2023/> | radius = 2.21<ref name=Waisberg2023/> | temperature = 8,200<ref name=Waisberg2023/> | gravity = 3.91<ref name=Gray2006/> | age_myr = 700<ref name=Waisberg2023/> | component2 = α² Lib B | mass2 = 1.79<ref name=Waisberg2023/> | radius2 = 1.92<ref name=Waisberg2023/> | temperature2= 7,930<ref name=Waisberg2023/> | age_myr2 = 700<ref name=Waisberg2023/> }} {{Starbox detail|no_heading=y | component1 = α¹ Lib A | mass = {{val|1.36|0.02}}<ref name=Luck2017/> | radius = 1.50<ref name=tic/> | luminosity = 3.83<ref name=Luck2017/> | temperature = {{val|6707|56|fmt=commas}}<ref name=Luck2017/> | metal_fe = −0.03<ref name=Luck2017/> | gravity = 4.23<ref name=Luck2017/> | rotational_velocity = 5.95<ref name=Luck2017/> | age_gyr = {{val|1.01|0.24}}<ref name=Luck2017/> | component2 = α¹ Lib B | mass2 = 0.5–0.6<ref name=Caballero2010/> }} {{Starbox catalog | names = {{odlist |name=Zubenelgenubi |name2=Kiffa Australis |name3=Lanx Australis |B=α Lib |WDS=J14509-1603 }} | component1 = α Lib B | names1 = {{odlist |B=α¹ Lib |F=8 Librae |BD=−15°3965 |FK5=1387 |HD=130819 |HIP=72603 |HR=5530 |SAO=158836 }}<ref name=SIMBAD1/> | component2 = α Lib A | names2 = {{odlist |B=α² Lib |F=9 Librae |BD=−15°3966 |FK5=548 |HD=130841 |HIP=72622 |HR=5531 |SAO=158840 }}<ref name=SIMBAD2/> }} {{Starbox reference |Simbad=alf01+Lib|sn=α¹ Lib |Simbad3=alf02+Lib|sn3=α² Lib }} {{Starbox end}} '''Alpha Librae''' ('''α Librae''', abbreviated '''Alpha Lib''', '''α Lib''') is a quadruple star system and, despite its '[[alpha]]' designation, it is the second-brightest star in the [[constellation]] of [[Libra (constellation)|Libra]]. The two components are designated '''α¹ Librae''' and '''α² Librae'''. The system bore the traditional name of '''Zubenelgenubi''' {{IPAc-en|z|uː|ˌ|b|ɛ|n|ɛ|l|dʒ|ɪ|ˈ|n|uː|b|i}},<ref name=Kunitzsch/> though the [[International Astronomical Union]] now regards that name as only applying to α² Librae.<ref name=IAU-CSN/>

Alpha² Librae is 0.33 degrees north of the [[ecliptic]] so it can be [[occultation|occulted]] by the [[Moon]] and (very rarely) by [[planet]]s. It was occulted by [[Venus]] on October 25, 1947;<ref name=Koennen1981/> the next occultation by a planet will be by [[Mercury (planet)|Mercury]] on 10 November 2052.<ref name=occultation>Peuschel, Marco (2003). [http://www.marco-peuschel.de/planetensterne.html "Astronomische Ereignisse der besonderen Art"] {{webarchive|url=https://web.archive.org/web/20050316042622/http://www.marco-peuschel.de/planetensterne.html |date=2005-03-16 }}. Retrieved July 10, 2005.</ref> Both components are eclipsed ([[occultation|occulted]]) by the sun from about 7–9 November.<ref>[http://in-the-sky.org/skymap.php?year=2019&month=November&day=9 In the Sky] Earth astronomy reference utility showing the ecliptic and relevant date as at J2000 - present</ref> Thus the star can be viewed the whole night, crossing the sky, in early May.

==Nomenclature== ''α Librae'' ([[Latinisation of names|Latinised]] to ''Alpha Librae'') is the system's [[Bayer designation]].

''Zubenelgenubi'' {{IPAc-en|,|z|u:|b|@n|E|l|dZ|@|'|n|u:|b|i}}, also rendered ''Zuben Elgenubi'', derives from the [[Arabic]] ّالزُبَانَى الجَنُوبِي ''al-zubānā al-janūbiyy'' "the southern claw", which was coined before Libra was recognized as a constellation distinct from [[Scorpius]]. The alternative name ''Kiffa Australis'' (''Elkhiffa Australis'') is a partial [[Latin]] translation of the Arabic ''al-kiffah al-janubiyyah'' ''الكفة الجنوبية'' "southern pan [of the scales]". Another name used in older astronomy texts, equivalent to "southern pan", was ''Lanx Australis''.<ref name=plhta/>

In 2016, the [[International Astronomical Union]] organized a [[IAU Working Group on Star Names|Working Group on Star Names]] (WGSN)<ref name=WGSN/> to catalogue and standardize proper names for stars. The WGSN approved the name ''Zubenelgenubi'' for ''α² Librae'' on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names.<ref name="IAU-CSN"/>

In [[Chinese astronomy|Chinese]], {{lang|zh|氐宿}} ({{lang|zh-Latn|Dī Xiù}}), meaning ''[[Root (Chinese constellation)|Root]]'', refers to an [[Asterism (astronomy)|asterism]] consisting of α² Librae, [[Iota Librae|ι Librae]], [[Gamma Librae|γ Librae]] and [[Beta Librae|β Librae]].<ref>{{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> Consequently, the [[Chinese star names|Chinese name]] for α² Librae itself is {{lang|zh|氐宿一}} ({{lang|zh-Latn|Dī Xiù yī}}), "the First Star of Root".<ref>{{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>

== Properties == <div style="float:left; width:240px; border:solid black 1px; text-align: center; margin: 8px; padding: 4px; font-size: 90%;"> {{tree chart/start}} {{tree chart|border=1| | |, |S1| |S1='''Aa''' }} {{tree chart|border=0| |, |( |PA| |PA=α² Lib (70.3 days) }} {{tree chart|border=1| |! |` |S2| |S2='''Ab''' }} {{tree chart|border=0| |( | |PD| | |PD=231″&nbsp;separation }} {{tree chart|border=1| |! |, |S3| | |S3='''Ba''' }} {{tree chart|border=0| |` |( |PB| | |PB=α¹ Lib (16.3 years) }} {{tree chart|border=1| | |` |S4| | |S4='''Bb''' }} {{tree chart/end}} Hierarchy of orbits in the α Librae system </div>

Alpha Librae is about {{Convert|77|ly|pc|abbr=off|lk=on}} from the [[Sun]]. The two brightest components of Alpha Librae form a [[double star]] moving together through space as [[common proper motion]] companions. They are separated in the sky by an [[angular size|angular distance]] of 231" (3'51"). The [[position angle]] of the companion is 314 degrees. The brighter of the two is a white star of [[stellar classification|spectral type]] A3, with an [[apparent magnitude]] of 2.8. Its companion is a type F4 star of apparent brightness 5.2. They are probably members of the [[Castor Moving Group]] of stars that have a similar motion through space and share a common origin some 200 million years ago.<ref name=Caballero2010/>

=== Alpha² Librae === The brightest member, α² Librae or α Librae A, is itself a [[spectroscopic binary]] system. The components have similar masses (mass ratio of 0.92) but the primary has a rotational velocity three times higher than its companion, which could be caused by them having significantly misaligned spin axes or if the primary is a merger product.<ref name=Waisberg2023/>

=== Alpha¹ Librae === The second member, α¹ Librae or α Librae B, is separated from the primary system by around {{val|5360|fmt=commas|ul=AU}}.<ref name=Waisberg2023/> It too is a spectroscopic binary with an orbital period of 5,870&nbsp;days and an [[angular separation]] of 0.383&nbsp;arcseconds;<ref name=soar2023/> equal to about 9&nbsp;au.<ref name=Waisberg2023/>

=== KU Librae === The system may have a fifth component, the star KU Librae at a separation of 2.6°, thus forming a hierarchical quintuple star system. KU Lib shares a similar motion through space to the Alpha Librae system, but is separated from the other stars by about a [[parsec]]. It is sufficiently close to be gravitationally bound to the other members,<ref name=Caballero2010/> but has a substantially different [[metallicity]], making it unlikely to be physically bound to the system.<ref name=Fuhrmann2015/>

== See also == * [[List of stars in Libra]]

==References== <references>

<ref name=SIMBAD1>{{cite simbad | title=* alf01 Lib | access-date=2007-01-23 }}</ref>

<ref name=SIMBAD2>{{cite simbad | title=* alf02 Lib | access-date=2007-01-23 }}</ref>

<ref name=hipparcos>{{cite journal | 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 |arxiv = 0708.1752 | s2cid=18759600 }}</ref>

<ref name=Waisberg2023>{{Cite journal |last1=Waisberg |first1=Idel |last2=Klein |first2=Ygal |last3=Katz |first3=Boaz |date=2023-08-23 |title=Hidden Companions to Intermediate-mass Stars. X. Solving for the Mass Ratio in the Spectroscopic Binary Zubenelgenubi = α ² Librae* |journal=Research Notes of the AAS |volume=7 |issue=8 |pages=180 |doi=10.3847/2515-5172/acf28f |bibcode=2023RNAAS...7..180W |issn=2515-5172|doi-access=free }}</ref>

<ref name=Caballero2010>{{cite journal | last1=Caballero | first1=J. A. | title=Reaching the boundary between stellar kinematic groups and very wide binaries. II. α Librae + KU Librae: a common proper motion system in Castor separated by 1.0 pc | journal=Astronomy and Astrophysics | volume=514 | page=A98 |date=May 2010 | doi=10.1051/0004-6361/200913986 | bibcode=2010A&A...514A..98C | arxiv=1001.5432 | s2cid=118875432 }}</ref>

<ref name=Fuhrmann2015>{{cite journal|bibcode=2015ApJ...809..107F|title=Multiplicity among F-type stars. II|journal=The Astrophysical Journal|volume=809|pages=107|last1=Fuhrmann|first1=K.|last2=Chini|first2=R.|year=2015|issue=1|doi=10.1088/0004-637X/809/1/107|s2cid=126218052 |doi-access=}}</ref>

<ref name=soar2023>{{cite journal |last1=Tokovinin |first1=Andrei |last2=Mason |first2=Brian D. |last3=Mendez |first3=Rene A. |last4=Costa |first4=Edgardo |title=Speckle Interferometry at SOAR Telescope in 2023 |journal=The Astronomical Journal |year=2024 |volume=168 |issue=1 |page=28 |doi=10.3847/1538-3881/ad4d56 |bibcode=2024AJ....168...28T |doi-access=free}}</ref>

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<ref name=Gray2006>{{cite journal | display-authors=1 | last1=Gray | first1=R. O. | last2=Corbally | first2=C. J. | last3=Garrison | first3=R. F. | last4=McFadden | first4=M. T. | last5=Bubar | first5=E. J. | last6=McGahee | first6=C. E. | last7=O'Donoghue | first7=A. A. | last8=Knox | first8=E. R. | title=Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample | journal=The Astronomical Journal | volume=132 | issue=1 | pages=161–170 |date=July 2006 | doi=10.1086/504637 | bibcode=2006AJ....132..161G |arxiv = astro-ph/0603770 | s2cid=119476992 }}</ref>

<ref name=Holmerg2009>{{cite journal | last1=Holmberg | first1=J. | last2=Nordström | first2=B. | last3=Andersen | first3=J. | title=The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics | journal=Astronomy and Astrophysics | volume=501 | issue=3 | pages=941–947 |date=July 2009 | doi=10.1051/0004-6361/200811191 | bibcode=2009A&A...501..941H |arxiv = 0811.3982 | s2cid=118577511 }}</ref>

<ref name=Zorec2012>{{Cite journal |last=Zorec |first=J. |last2=Royer |first2=F. |date=January 2012 |title=Rotational velocities of A-type stars. IV. Evolution of rotational velocities |bibcode=2012A&A...537A.120Z |journal=Astronomy and Astrophysics |language=en |volume=537 |pages=A120 |doi=10.1051/0004-6361/201117691 |issn=0004-6361}}</ref>

<ref name=Takeda2018>{{Cite journal |last=Takeda |first=Yoichi |last2=Kawanomoto |first2=Satoshi |last3=Ohishi |first3=Naoko |last4=Kang |first4=Dong-Il |last5=Lee |first5=Byeong-Cheol |last6=Kim |first6=Kang-Min |last7=Han |first7=Inwoo |date=October 2018 |title=Photospheric carbon, nitrogen, and oxygen abundances of A-type main-sequence stars |bibcode=2018PASJ...70...91T |journal=Publications of the Astronomical Society of Japan |language=en |volume=70 |issue=5 |pages=91 |doi=10.1093/pasj/psy091 |issn=0004-6264|arxiv=1807.06265 }}</ref>

<ref name=sps1966>{{cite journal | display-authors=1 | last1=Gutierrez-Moreno | first1=Adelina | last2=Moreno | first2=H. | last3=Stock | first3=J. | last4=Torres | first4=C. | last5=Wroblewski | first5=H. | title=A System of photometric standards | journal=Publ. Dept. Astron. Univ. Chile | publisher=Publicaciones Universidad de Chile, Department de Astronomy | volume=1 | pages=1–17 | date=1966 | bibcode=1966PDAUC...1....1G }}</ref>

<ref name=Luck2017>{{Cite journal |last=Luck |first=R. Earle |date=2018-03-01 |title=Abundances in the Local Region. III. Southern F, G, and K Dwarfs |bibcode=2018AJ....155..111L |journal=The Astronomical Journal |volume=155 |issue=3 |pages=111 |doi=10.3847/1538-3881/aaa9b5 |doi-access=free |issn=0004-6256}} [https://vizier.cds.unistra.fr/viz-bin/VizieR?-source=J/AJ/155/111&ID=*%20alf01%20Lib Alpha1 Librae's database entry] at [[VizieR]].</ref>

<ref name=mk>{{cite journal|bibcode=1988mcts.book.....H|title=Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Volume 4, Declinations -26°.0 to -12°.0|journal=Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Volume 4|last1=Houk|first1=N.|last2=Smith-Moore|first2=M.|year=1988}}</ref>

<ref name=Fuhrmann2014>{{cite journal|bibcode=2014MNRAS.437.2303F|title=On the bright A-type star Alpha Librae A|journal=Monthly Notices of the Royal Astronomical Society|volume=437|issue=3|pages=2303|last1=Fuhrmann|first1=K.|last2=Chini|first2=R.|last3=Barr|first3=A.|last4=Buda|first4=L.-S.|last5=Kaderhandt|first5=L.|last6=Pozo|first6=F.|last7=Ramolla|first7=M.|year=2014|doi=10.1093/mnras/stt2046|doi-access=free}}</ref>

<ref name=Koennen1981>{{cite journal | title=Planetary occultations of bright stars. | last1=Können | first1=G. P. | last2=Van Maanen | first2=J. | journal=Journal of the British Astronomical Association | volume=91 | pages=148–157 | date=April 1981 | bibcode=1981JBAA...91..148K }}</ref>

<ref name=ap1999>{{cite journal |last1=Allende Prieto |first1=C. |last2=Lambert |first2=D. L. |title=Fundamental parameters of nearby stars from the comparison with evolutionary calculations: Masses, radii and effective temperatures |journal=Astronomy and Astrophysics |date=1999 |volume=352 |page=555 |arxiv=astro-ph/9911002 |bibcode=1999A&A...352..555A }}</ref>

<ref name=plhta>[https://archive.org/stream/tabulaeastronom00suntgoog#page/n146/mode/2up Philippe La Hire, "Tabulae Astronomicae" (1727), see star table, page 13.]</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=IAU-CSN>{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt | title=IAU Catalog of Star Names |access-date=28 July 2016}}</ref>

<ref name=EgUBV>{{cite journal|author1=Mermilliod, J.-C.|title=Compilation of Eggen's UBV data, transformed to UBV (unpublished)|journal=Catalogue of Eggen's UBV Data|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1986EgUBV........0M&db_key=AST&nosetcookie=1|date=1986|bibcode= 1986EgUBV........0M }}</ref>

<ref name=WGSN>{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN) | publisher=[[International Astronomical Union]] | access-date=22 May 2016 }}</ref>

</references>

==External links== *Kaler, Jim (2004). [https://web.archive.org/web/20050818161632/http://www.astro.uiuc.edu/~kaler/sow/zubenel.html "STARS: Zubenelgenubi"]. Retrieved July 10, 2005. * {{WikiSky}}

{{Stars of Libra}} {{Sky|14|50|41.26|-|15|59|49.5|77}}

[[Category:Bayer objects|Librae, Alpha]] [[Category:Multiple star systems|4]] [[Category:Libra (constellation)]] [[Category:A-type main-sequence stars]] [[Category:F-type main-sequence stars]] [[Category:M-type main-sequence stars]] [[Category:Stars with proper names|Zubenelgenubi]] [[Category:Castor Moving Group]] [[Category:Flamsteed objects|Librae, 08 9]] [[Category:Hipparcos objects|072603 22]] [[Category:Bright Star Catalogue objects|5530 1]] [[Category:Henry Draper Catalogue objects|130819 41]] [[Category:Durchmusterung objects|BD-15 3965]] [[Category:Am stars]] [[Category:Objects with variable star designations|Librae, KU]]