Editing Alpha Librae

{{short description|Binary 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  = α<sup>1</sup> Lib
 | ra1         = {{RA|14|50|41.18097}}<ref name=aaa474_2_653/>
 | dec1        = {{DEC|-15|59|50.0482}}<ref name=aaa474_2_653/>
 | appmag_v1   = +5.153<ref name=sps1966/>
 | component2  = α<sup>2</sup> Lib
 | ra2         = {{RA|14|50|52.71309}}<ref name=aaa474_2_653/>
 | dec2        = {{DEC|-16|02|30.3955}}<ref name=aaa474_2_653/>
 | appmag_v2   = +2.741<ref name=sps1966/>
}}
{{Starbox character
 | component = α<sup>1</sup> Lib
 | class       = F3 V<ref name=mk/>
 | b-v         = +0.39<ref name=EgUBV/>
 | u-b         = −0.02<ref name=EgUBV/>
 | variable    = 
}}
{{Starbox character|no_heading=y
 | component =  α<sup>2</sup> Lib
 | class       = kA2hA5mA4 IV-V<ref name=apj132_1_161/>
 | b-v         = +0.15<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{{cite journal|author1=Mermilliod, J.-C.|title=Compilation of Eggen's UBV data, transformed to UBV (unpublished)|journal=Catalogue of Eggen's UBV Data|url=http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?1986EgUBV........0M&db_key=AST&nosetcookie=1|date=1986|bibcode=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>
 | u-b         = +0.10<ref name=EgUBV/>
 | variable    = 
}}
{{Starbox astrometry
 | component1  = α<sup>1</sup> Lib
 | radial_v    = −23.47<ref name=orbit/>
 | prop_mo_ra  = −136.27<ref name=aaa474_2_653/>
 | prop_mo_dec = −59.04<ref name=aaa474_2_653/>
 | parallax    = 43.52
 | p_error     = 0.43
 | parallax_footnote = <ref name=aaa474_2_653/>
 | absmag_v    = +3.35<ref name=aaa501_3_941/>
 | component2 = α<sup>2</sup> Lib
 | radial_v2 = 
 | prop_mo_ra2 = −105.68<ref name=aaa474_2_653/>
 | prop_mo_dec2 = −68.40<ref name=aaa474_2_653/>
 | parallax2 = 43.03
 | p_error2 = 0.19
 | parallax_footnote2 = <ref name=aaa474_2_653/>
 | absmag_v2 =
}}
{{Starbox orbit
| reference = <ref name=orbit/>
| primary = α<sup>2</sup> Lib A
| name = α<sup>2</sup> Lib B
| period_unitless = 70.34 days
| eccentricity = 0.41
| axis_unitless = 0.51 au
| k2 = 43.1
}}
{{Starbox detail
 | component1  = α<sup>1</sup> Lib A
 | mass        = {{val|1.36|0.02}}<ref name="luck"/>
 | radius      = {{solar radius calculator|type=logLT|0.55|6707|decimals=2}}0<ref name="luck"/>{{efn|name=radius}}
 | luminosity  = 3.55<ref name="luck"/>
 | temperature = {{val|6707|56|fmt=commas}}<ref name="luck"/>
 | metal_fe    = {{val|-0.03}}<ref name="luck"/>
 | gravity     = 4.27<ref name="luck"/>
 | rotational_velocity = 5.95<ref name="luck"/>
 | age_gyr     = {{val|1.01|0.24}}<ref name="luck"/>
 | component2  = α<sup>1</sup> Lib B
 | mass2 = 0.5–0.6<ref name=aaa514_A98/>
}}
{{Starbox detail|no_heading=y
 | component1 = α<sup>2</sup> Lib A
 | mass = 1.95<ref name=waisberg/>
 | radius = 2.21<ref name=waisberg/>
 | temperature = 8,200<ref name=waisberg/>
 | gravity = 3.91<ref name=apj132_1_161/>
 | component2 = α<sup>2</sup> Lib B
 | mass2 = 1.79<ref name=waisberg/>
 | radius2 = 1.92<ref name=waisberg/>
 | temperature2 = 7,930<ref name=waisberg/>
}}
{{Starbox catalog
 | names = Zubenelgenubi, Kiffa Australis, Lanx Australis, α Lib.
 | component1 = α<sup>1</sup> Lib
 | names1 = 8 Librae, [[Bonner Durchmusterung|BD]]−15&nbsp;3965, [[FK5]]&nbsp;1387, [[Henry Draper Catalogue|HD]]&nbsp;130819, [[Hipparcos catalogue|HIP]]&nbsp;72603, [[Bright Star Catalogue|HR]]&nbsp;5530, [[Smithsonian Astrophysical Observatory Star Catalogue|SAO]]&nbsp;158836.<ref name=SIMBAD1/>
 | component2 = α<sup>2</sup> Lib
 | names2 = 9 Librae, [[Bonner Durchmusterung|BD]]−15&nbsp;3966, [[FK5]]&nbsp;548, [[Henry Draper Catalogue|HD]]&nbsp;130841, [[Hipparcos catalogue|HIP]]&nbsp;72622, [[Bright Star Catalogue|HR]]&nbsp;5531, [[Smithsonian Astrophysical Observatory Star Catalogue|SAO]]&nbsp;158840.<ref name=SIMBAD2/>
}}
{{Starbox reference
|Simbad=alf+Lib|sn=α Lib
|Simbad2=alf01+Lib|sn2=α<sup>1</sup> Lib
|Simbad3=alf02+Lib|sn3=α<sup>2</sup> Lib
}}
{{Starbox end}}
'''Alpha Librae''' ('''α Librae''', abbreviated '''Alpha Lib''', '''α Lib''') is a [[double star]] and, despite its '[[alpha]]' designation, it is the second-brightest star system (or star) in the [[constellation]] of [[Libra (constellation)|Libra]]. The two components are designated '''α<sup>1</sup> Librae''' and '''α<sup>2</sup> 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>{{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> though the [[International Astronomical Union]] now regards that name as only applying to α<sup>2</sup> Librae.<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>

Alpha<sup>2</sup> 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>[https://archive.org/stream/tabulaeastronom00suntgoog#page/n146/mode/2up Philippe La Hire, "Tabulae Astronomicae" (1727), see star table, page 13.]</ref>

In 2016, the [[International Astronomical Union]] organized a [[IAU Working Group on Star Names|Working Group on Star Names]] (WGSN)<ref name="WGSN">{{citation
 | 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 | postscript=. }}</ref> to catalogue and standardize proper names for stars. The WGSN approved the name ''Zubenelgenubi'' for ''α<sup>2</sup> 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 α<sup>2</sup> 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 α<sup>2</sup> 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 ==
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=aaa514_A98/>

=== Alpha<sup>2</sup> Librae ===
The brightest member, α<sup>2</sup> Librae, 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=waisberg>{{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 <sup>2</sup> 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> 
=== Alpha<sup>1</sup> Librae ===
The second member, α<sup>1</sup> Librae, is separated from the primary system by around {{val|5400|ul=AU}}. It too is a spectroscopic binary with an orbital period of 5,870&nbsp;days and an [[angular separation]] of 0.383&nbsp;arcseconds; equal to about 10&nbsp;AU. 
=== 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=aaa514_A98/> but has a substantially different [[metallicity]], making it unlikely to be physically bound to the system.<ref name=multiplicity/>

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

== Notes ==
{{Notelist|notes=

{{Efn|name=radius|1=Calculated, using the [[Stefan-Boltzmann law]] and the star's [[effective temperature]] and luminosity, with respect to the [[Sun|solar]] nominal effective temperature of 5,772&nbsp;[[Kelvin|K]]:<math display="block">\sqrt{\biggl(\frac{5,772}{6,707}\biggr)^4 \cdot 10^{0.55}} = 1.40\ R_\odot.</math>}}

}}

==References==
{{reflist|refs=

<ref name=multiplicity>{{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=aaa474_2_653>{{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 |arxiv = 0708.1752 | s2cid=18759600 }}</ref>

<ref name=apj132_1_161>{{citation | 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=aaa501_3_941>{{citation | 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=sps1966>{{citation | 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=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=aaa514_A98>{{citation | 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="luck">{{Citation |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=orbit>{{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>

}}

==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}}
{{Sky|14|50|41.26|-|15|59|49.5|77}}

{{Stars of Libra}}

{{DEFAULTSORT:Alpha Librae}}
[[Category:Bayer objects|Librae, Alpha]]
[[Category:Binary stars]]
[[Category:Libra (constellation)]]
[[Category:A-type subgiants]]
[[Category:F-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:A-type main-sequence stars]]