View source for Acrux

{{Short description|Star in the constellation Crux}}
{{About|the star|the Christian college|Alphacrucis|research ship|Alpha Crucis (research vessel)}}
{{Starbox begin}}
{{Starbox image
| image=[[File:Acrux kstars.png|250px]]
| caption=The position of Acrux
}}
{{Starbox observe
| pronounce= {{IPAc-en|'|ei|k|r|V|k|s}}{{citation needed|date=May 2022}}
| epoch    = J2000
| constell = [[Crux]]
| ra       = {{RA|12|26|35.89522}}<ref name=aaa474_2_653/>
| dec      = {{DEC|−63|05|56.7343}}<ref name=aaa474_2_653/>
| appmag_v = 0.76<ref name=corben>{{cite journal|bibcode=1966MNSSA..25...44C|title=Photoelectric magnitudes and colours for bright southern stars|journal=Monthly Notes of the Astron. Soc. Southern Africa|volume=25|pages=44|last1=Corben|first1=P. M.|year=1966}}</ref> (1.33 + 1.75)<ref name="Tokovinin1997">{{cite journal|last1=Tokovinin|first1=A. A.|title=MSC - a catalogue of physical multiple stars|journal=Astronomy and Astrophysics Supplement Series|volume=124|issue=1|year=1997|pages=75–84|issn=0365-0138|doi=10.1051/aas:1997181|bibcode = 1997A&AS..124...75T |doi-access=free}}</ref>
}}
{{Starbox character
| class    = B0.5IV + B1V<ref name=houk1979/>
| b-v      = −0.26<ref name=corben/>
| u-b      =
| variable = [[Beta Cephei variable|β Cep]]<ref name=Sharma>{{cite journal|doi=10.1093/mnras/stac1816 |title=Pulsating B stars in the Scorpius–Centaurus Association with TESS |year=2022 |last1=Sharma |first1=Awshesh N. |last2=Bedding |first2=Timothy R. |last3=Saio |first3=Hideyuki |last4=White |first4=Timothy R. |journal=Monthly Notices of the Royal Astronomical Society |volume=515 |issue=1 |pages=828–840 |doi-access=free |arxiv=2203.02582 | bibcode=2022MNRAS.515..828S}}</ref>
}}
{{Starbox astrometry
| radial_v = −11.2 / −0.6<ref name=gcsrv53/>
| prop_mo_ra  = −35.83<ref name=aaa474_2_653/>
| prop_mo_dec = −14.86<ref name=aaa474_2_653/>
| gal_lat  = -00.3627
| gal_lon  = 300.1266
| parallax = 10.13
| p_error  = 0.50
| parallax_footnote = <ref name=aaa474_2_653/>
| absmag_v = −3.77<ref name=kaltcheva>{{cite journal|bibcode= 2014A&A...562A..69K|title= Massive stellar content of the Galactic supershell GSH 305+01-24|journal= Astronomy & Astrophysics|volume= 562|pages= A69|last1= Kaltcheva|first1= N. T.|last2= Golev|first2= V. K.|last3= Moran|first3= K.|year= 2014|doi= 10.1051/0004-6361/201321454|arxiv = 1312.5592 |s2cid= 54222753}}</ref> {{nowrap|(−2.2 + −2.7<ref>{{cite journal|bibcode=1953PASP...65...30V|title=The Twenty Brightest Stars|journal=Publications of the Astronomical Society of the Pacific|volume=65|issue=382|pages=30|last1=Van De Kamp|first1=Peter|year=1953|doi=10.1086/126523|doi-access=free}}</ref>)}}
}}
{{Starbox orbit
| reference=<ref name=Thackeray1980>{{citation
 | last1=Thackeray | first1=A. D. | last2=Wegner | first2=G.
 | title=An improved spectroscopic orbit for α<sup>1</sup> Crucis
 | journal=Monthly Notices of the Royal Astronomical Society
 | volume=191 | issue=2 | pages=217–220 | date=April 1980
 | doi=10.1093/mnras/191.2.217 | bibcode=1980MNRAS.191..217T| doi-access= free}}</ref>
| name=α Crucis Ab
| period_unitless = {{Val|75.7794|0.0037|u=day}}
| eccentricity = {{Val|0.46|0.03}}
| periarg = {{Val|21|6}}
| periastron = {{Val|2417642.3|1.6|fmt=commas|u=JD}}
| k1 = {{Val|41.7|1.2}}
|primary=α Crucis Aa}}
{{Starbox detail
| component1 = α<sup>1</sup>
| metal_fe =
| mass     = 17.80 + 6.05<ref name="Tokovinin1997"/>
| radius   = {{solar radius calculator|type=logLT|1=4.52|logLerr=0.04|2=28840|Terr=0|decimals=2}}<ref name=Sharma/>{{efn | name=radius | Applying the [[Stefan–Boltzmann law]] with a nominal [[sun|solar]] [[effective temperature]] of 5,772&nbsp;[[Kelvin|K]]: 
:<math>\sqrt{\biggl(\frac{5,772}{28,840}\biggr)^4 \cdot 10^{4.52}} = 7.289\ R_\odot</math>.}}
| rotation =
| luminosity = {{val|31,110|3190|2910|fmt=commas}}<ref name=Sharma/>
| rotational_velocity = 124<ref name=Sharma/>
| temperature = 28,840<ref name=Sharma/>
| component2 = α<sup>2</sup>
| metal_fe2 =
| mass2    = 15.52<ref name="Tokovinin1997"/>
| radius2  = {{solar radius calculator|type=AD|0.52|0.099|decimals=2}}<ref name=lang2006/>
| luminosity2 = 16,000<ref name=kaler/>
| rotational_velocity2 = 200<ref name=dravins>{{cite book|bibcode=2010SPIE.7734E..0AD|arxiv=1009.5815|title=Optical and Infrared Interferometry II|series=Proceedings of the SPIE|volume=7734|pages=77340A|last1=Dravins|first1=Dainis|last2=Jensen|first2=Hannes|last3=Lebohec|first3=Stephan|last4=Nuñez|first4=Paul D.|chapter=Stellar intensity interferometry: Astrophysical targets for sub-milliarcsecond imaging |year=2010|doi=10.1117/12.856394|s2cid=55641060}}</ref>
| temperature2 = 28,000<ref name=dravins/>
| age_myr2 = 10.8<ref name=tetzlaff>{{cite journal|bibcode= 2011MNRAS.410..190T|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|last1= Tetzlaff|first1= N.|last2= Neuhäuser|first2= R.|last3= Hohle|first3= M. M.|year= 2011|doi= 10.1111/j.1365-2966.2010.17434.x|doi-access= free|arxiv = 1007.4883 |s2cid= 118629873}}</ref>
}}
{{Starbox catalog
| names = {{odlist | B=α Crucis | HIP=60718 | CPD=−62°2745 | WDS=J12266-6306 | CCDM=J12266-6306 }}
| component1 = α<sup>1</sup> Cru
| names1 = {{odlist | name=[[List of proper names of stars|Acrux]] | HR=4730 | HD=108248 | FK5=462 | GC=16952 | name2=[[Gould designation|26&nbsp;G.]]&nbsp;Crucis }}
| component2 = α<sup>2</sup> Cru
| names2 = {{odlist | HR=4731 | HD=108249 | GC=16953 | 2MASS=J12263615-6305571 | name=[[Gould designation|27&nbsp;G.]]&nbsp;Crucis }}
}}
{{Starbox reference
| Simbad=CCDM+J12266-6306AB | sn=α Cru
| Simbad2=*+alf01+Cru | sn2=α<sup>1</sup> Cru
| Simbad3=*+alf02+Cru | sn3=α<sup>2</sup> Cru
}}
{{Starbox end}}

'''Acrux''' is the brightest [[star]] in the southern [[constellation]] of [[Crux]]. It has the [[Bayer designation]] '''α Crucis''', which is [[Latinisation of names|Latinised]] to '''Alpha Crucis''' and abbreviated '''Alpha Cru''' or '''α Cru'''. With a combined [[visual magnitude]] of +0.76, it is the [[list of brightest stars|13th-brightest star]] in the [[night sky]].<!-- Acrux can be passed in brightness by Aldebaran and Enif (ε Pegasi), and Betelgeuse can fall behind Acrux in brightness.--> It is the most southerly star of the [[Asterism (astronomy)|asterism]] known as the Southern Cross and is the southernmost [[first-magnitude star]], 2.3 degrees more southerly than [[Alpha Centauri]].<ref>{{cite book|last1=Bordeleau|first1=André G.|chapter=Federative Republic of Brazil: Constellations in the Breeze|title=Flags of the Night Sky|date=12 August 2013|pages=1–72|doi=10.1007/978-1-4614-0929-8_1|publisher=Springer|location=New York|isbn=978-1-4614-0928-1}}</ref> This system is located at a distance of 321 [[light-year]]s from the [[Sun]].<ref name=aaa474_2_653/><ref name=GSM/>

To the naked eye Acrux appears as a single star, but it is actually a multiple star system containing six components. Through optical [[telescope]]s, Acrux appears as a [[triple star system|triple star]], whose two brightest components are visually separated by about 4 [[arcsecond]]s and are known as Acrux A and Acrux B, α<sup>1</sup> Crucis and α<sup>2</sup> Crucis, or α Crucis A and α Crucis B. Both components are [[B-type star]]s, and are many times more massive and luminous than the Sun. This system was the second ever to be recognized as a binary, in 1685 by a [[Jesuit priest]].<ref>{{cite web | url=https://cfah.org.za/outreach/crux/ | title=A Story about Crux &#124; Centre for Astronomical Heritage (CfAH) }}</ref> α<sup>1</sup> Crucis is itself a [[spectroscopic binary]] with components designated α Crucis Aa (officially named '''Acrux''', historically the name of the entire system)<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=21 November 2016}}</ref> and α Crucis Ab. Its two component stars orbit every 76 days at a separation of about 1 [[astronomical unit]] (AU).<ref name=kaler/> [[HR 4729]], also known as Acrux C, is a more distant companion, forming a triple star through small telescopes. C is also a spectroscopic binary, which brings the total number of stars in the system to at least five.

==Nomenclature==

[[File:Deep Crux wide field with fog.jpg|thumb|left|The constellation [[Crux]]]]
''α Crucis'' (Latinised to ''Alpha Crucis'') is the system's [[Bayer designation]]; ''α<sup>1</sup>'' and ''α<sup>2</sup> Crucis'', those of its two main components stars. The designations of these two constituents as ''Acrux A'' and ''Acrux B'' and those of ''A's'' components—''Acrux Aa'' and ''Acrux Ab''—derive from the convention used by the [[Washington Multiplicity Catalog]] (WMC) for multiple star systems,{{dubious|date=April 2019}} and adopted by the [[International Astronomical Union]] (IAU).<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>{{Unreliable source?|date=April 2019|reason=This is only a proposal, but wasn't ratified. WDS is the adopted usage here.}}

The historical name ''Acrux'' for ''α<sup>1</sup> Crucis'' is an "[[American English|Americanism]]" coined in the 19th century, but entering common use only by the mid 20th century.<ref>''Memoirs of the Rev. Walter M. Lowrie: missionary to China'' (1849), p. 93. Described as an "Americanism" in ''The Geographical Journal'', vol. 92, Royal Geographical Society, 1938.</ref>{{Better source needed|date=April 2019|reason=Acrux was named by American Elijah H. Burritt in the 1850s}} In 2016, the [[International Astronomical Union]] organized a [[IAU Working Group on Star Names|Working Group on Star Names]] (WGSN)<ref name="WGSN">{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN)|access-date=22 May 2016}}</ref> to catalog and standardize proper names for stars. The WGSN states that in the case of [[Star system|multiple stars]] the name should be understood to be attributed to the brightest component by visual brightness.<ref name="WGSN2">{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin2.pdf | title=Bulletin of the IAU Working Group on Star Names, No. 2 |access-date=12 October 2016}}</ref> The WGSN approved the name ''Acrux'' for the star ''Acrux Aa'' on 20 July 2016 and it is now so entered in the IAU Catalog of Star Names.<ref name="IAU-CSN"/>

Since Acrux is at −63° [[declination]], making it the southernmost first-magnitude star, it is only visible south of [[latitude]] 27° North. It barely rises from cities such as [[Miami]], [[United States]], or [[Karachi]], [[Pakistan]] (both around 25°N) and not at all from [[New Orleans]], [[United States]], or [[Cairo]], [[Egypt]] (both about 30°N). Because of Earth's [[axial precession]], the star was visible to ancient [[Hindu]] astronomers in [[India]] who named it ''Tri-shanku''. It was also visible to the [[ancient Romans]] and [[Ancient Greece|Greeks]], who regarded it as part of the constellation of [[Centaurus]].<ref>Richard Hinckley Allen, ''Star Names: Their Lore and Meaning,'' Dover Books, 1963.</ref>

In [[Chinese language|Chinese]], {{lang|zh|十字架}} ({{lang|zh-Latn|Shí Zì Jià}}, "[[Chinese constellations#The Southern Asterisms (近南極星區)|Cross]]"), refers to an asterism consisting of Acrux, [[Mimosa (star)|Mimosa]], [[Gamma Crucis]] and [[Delta Crucis]].<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, Acrux itself is known as {{lang|zh|十字架二}} ({{lang|zh-Latn|Shí Zì Jià èr}}, "the Second Star of Cross").<ref>{{in lang|zh}} [http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_a_al.htm 香港太空館 - 研究資源 - 亮星中英對照表] {{webarchive|url=https://web.archive.org/web/20100903162121/http://www.lcsd.gov.hk/CE/Museum/Space/Research/StarName/c_research_chinengstars_a_al.htm |date=2010-09-03 }}, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref>

This star is known as ''Estrela de Magalhães'' ("Star of [[Magellan]]") in [[Portuguese language|Portuguese]].<ref>{{cite journal|doi=10.1590/S1806-11172008000100007 |title=Transformação de coordenadas aplicada à construção da maquete tridimensional de uma constelação |journal=Revista Brasileira de Ensino de Física |volume=30 |pages=1306.1–1306.7 |year=2008 |last1=Silva |first1=Guilherme Marques dos Santos |last2=Ribas |first2=Felipe Braga |last3=Freitas |first3=Mário Sérgio Teixeira de |doi-access=free }}</ref>

==Stellar properties==
[[File:Acrux.png|thumb|left|α Crucis with the nearby [[HR 4729|HD 108250]] (the 2nd-brightest star)]]
The two components, α<sup>1</sup> and α<sup>2</sup> Crucis, are separated by 4 [[arcseconds]]. α<sup>1</sup> is magnitude 1.40 and α<sup>2</sup> is magnitude 2.09, both early [[stellar classification|class B]] stars, with surface temperatures of about 28,000 and {{Val|26000|fmt=commas|ul=K}}, respectively. Their luminosities are 25,000 and 16,000 times [[Solar luminosity|that of the Sun]]. α<sup>1</sup> and α<sup>2</sup> orbit over such a long period that motion is only barely seen. From their minimum separation of 430 astronomical units, the period is estimated to be around 1,500 years.<ref name="Tokovinin1997"/>

α<sup>1</sup> is itself a spectroscopic [[binary star]], with its components thought to be around 14 and 10 times the [[mass of the Sun]] and orbiting in only 76 days at a separation of about {{Val|1|ul=AU}}. The masses of α<sup>2</sup> and the brighter component of α<sup>1</sup> suggest that the stars will someday expand into [[Blue supergiant|blue]] and [[red supergiants]] (similar to [[Betelgeuse]] and [[Antares]]) before exploding as [[supernova]]e.<ref name=kaler>{{cite book|doi=10.1007/0-387-21625-1_2|chapter=Acrux|title=The Hundred Greatest Stars|pages=4–5|year=2002|isbn=978-0-387-95436-3|last1=Kaler|first1=James B.}}</ref> Component Ab may perform electron capture in the degenerate O+Ne+Mg core and trigger a supernova explosion,<ref name=nomoto/><ref>{{cite journal |last1=S. E. Woosley, Alexander Heger |title=The Remarkable Deaths of 9 - 11 Solar Mass Stars |journal=Astrophysics |date=May 25, 2015 |volume=810 |issue=1 |page=34 |doi=10.1088/0004-637X/810/1/34 |arxiv=1505.06712 |bibcode=2015ApJ...810...34W |s2cid=119163256 }}</ref> otherwise it will become a massive white dwarf.<ref name=kaler>{{cite book|doi=10.1007/0-387-21625-1_2|chapter=Acrux|title=The Hundred Greatest Stars|pages=4–5|year=2002|isbn=978-0-387-95436-3|last1=Kaler|first1=James B.}}</ref>

Photometry with the [[TESS]] satellite has shown that one of the stars in the α Crucis system is a [[Beta Cephei variable|β Cephei variable]], although α<sup>1</sup> and α<sup>2</sup> Crucis are too close for TESS to resolve and determine which one is the pulsator.<ref name=Sharma/>

Rizzuto and colleagues determined in 2011 that the α Crucis system was 66% likely to be a member of the Lower Centaurus–Crux sub-group of the [[Scorpius–Centaurus association]]. It was not previously seen to be a member of the group.<ref name="mnras416_3108">{{citation | last1=Rizzuto | first1=Aaron | last2=Ireland| first2=Michael | last3=Robertson | first3=J. G. | title=Multidimensional Bayesian membership analysis of the Sco OB2 moving group | journal=Monthly Notices of the Royal Astronomical Society |date=October 2011 | volume=416 | issue=4 | pages=3108–3117 | doi=10.1111/j.1365-2966.2011.19256.x | doi-access=free | bibcode=2011MNRAS.416.3108R | arxiv=1106.2857 | s2cid=54510608 | postscript=. }}</ref> A [[bow shock]] is present around α Crucis, and is visible in the [[infrared]] spectrum, but is not aligned with α Crucis; the bow shock likely formed from large-scale motions in the interstellar matter.<ref>{{cite journal | doi=10.52526/25792776-24.71.1-42 | title=The runaway nature and origin of α Crucis system | date=2024 | last1=Torosyan | first1=M. | last2=Azatyan | first2=N. | last3=Nikoghosyan | first3=E. | last4=Samsonyan | first4=A. | last5=Andreasyan | first5=D. | journal=Communications of the Byurakan Astrophysical Observatory | volume=71 | pages=42–47 | arxiv=2407.09934 | bibcode=2024CoBAO..71...42T }}</ref>

The cooler, less-luminous B-class star [[HR 4729]] (HD 108250) lies 90 arcseconds away from triple star system α Crucis and shares its motion through space, suggesting it may be gravitationally bound to it, and it is therefore generally assumed to be physically associated.<ref>{{cite journal|last1=Shatsky|first1=N. |last2=Tokovinin|first2=A. |title=The mass ratio distribution of B-type visual binaries in the Sco OB2 association|journal=Astronomy and Astrophysics|date=2002|volume=382|pages=92–103|arxiv = astro-ph/0109456 |bibcode = 2002A&A...382...92S |doi = 10.1051/0004-6361:20011542 |s2cid=16697655 }}</ref><ref>{{cite journal|last1=Eggleton|first1=Peter|last2=Tokovinin|first2=A. |title=A catalogue of multiplicity among bright stellar systems|journal=[[Monthly Notices of the Royal Astronomical Society]]|date=2008|volume=389|issue=2|pages=869–879|arxiv = 0806.2878 |bibcode = 2008MNRAS.389..869E |doi = 10.1111/j.1365-2966.2008.13596.x |doi-access=free |s2cid=14878976}}</ref> It is itself a spectroscopic binary system, sometimes catalogued as component C (Acrux C) of the Acrux multiple system. Another fainter visual companion listed as component D or Acrux D. A further seven faint stars are also listed as companions out to a distance of about two arc-minutes.<ref name="wds">{{cite journal|bibcode= 2001AJ....122.3466M|title= The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog|journal= The Astronomical Journal|volume= 122|issue= 6|pages= 3466–3471|last1= Mason|first1= Brian D.|last2= Wycoff|first2= Gary L.|last3= Hartkopf|first3= William I.|last4= Douglass|first4= Geoffrey G.|last5= Worley|first5= Charles E.|year= 2001|doi= 10.1086/323920|doi-access= free}}</ref>

On 2 October 2008, the [[Cassini–Huygens]] spacecraft resolved three of the components (A, B and C) of the multiple star system as [[Saturn]]'s disk occulted it.<ref>{{cite web|publisher=NASA/JPL/Space Science Institute |url=https://saturn.jpl.nasa.gov/raw_images/197551/ |title=Cassini raw image|work=Cassini: The Grand Finale |access-date=2017-10-31 }}</ref><ref>[http://www.unmannedspaceflight.com/index.php?showtopic=1809&view=findpost&p=127561 Cassini "Kodak Moments" - Unmanned Spaceflight.com]. Retrieved 2008-10-21</ref>

{|class="wikitable"
|+Acrux system
!colspan=4|
!Separation<br />([[minute and second of arc|arcsec]])
!Projected<br />separation<br />([[astronomical unit|AU]])
!Orbital<br />period
![[stellar classification|Spectral<br />type]]
!Mass<br />([[solar mass|M<sub>☉</sub>]])
![[apparent magnitude|App. mag.]]<br />(V)
|-
|align=center rowspan=6| Acrux ABC ||align=center rowspan=3 style="background-color: #EEEEEE"| [[HR 4729]] ABC<br />(Acrux C & CP)<br /><ref group="orbit note" name="orbit">HR 4729 and Acrux A are separated by 90 arcseconds, resulting in a projected separation of 9400 AU/0.15 light years. This combined binary system has an estimated orbital period of 120,000 years.</ref> ||align=center colspan=2 style="background-color: #EEEEEE"| α<sup>1</sup> Crucis CP ||align=center style="background-color: #EEEEEE"| 2.1 ||align=center style="background-color: #EEEEEE"| 220 ||align=center style="background-color: #EEEEEE"| 930 years ||align=center style="background: {{star-color|M}}; | M0V ||align=center| 0.47 ||align=center| 15.0
|-
|align=center rowspan=2 style="background-color: #CCCCCC"| HR 4729 AB ||align=center style="background-color: #CCCCCC"| HR 4729 A ||rowspan=2 align=center style="background-color: #CCCCCC"| 0.00046 ||rowspan=2 align=center style="background-color: #CCCCCC"| 0.048 ||rowspan=2 align=center style="background-color: #CCCCCC"| 1.225 days ||align=center style="background: {{star-color|B}}; | B4V ||align=center| 8.68 ||align=center rowspan=2| 4.9<br />(combined)
|-
|align=center style="background-color: #CCCCCC"| HR 4729 B ||align=center style="background: {{star-color|G}}; | G?V ||align=center| 0.97
|-
|align=center rowspan=3 style="background-color: #DDDDDD"| Acrux AB<br />(α<sup>1</sup> and α<sup>2</sup>)<br /><ref group="orbit note" name="orbit"/> ||align=center colspan=2 style="background-color: #DDDDDD"| α<sup>2</sup> Crucis ||align=center style="background-color: #DDDDDD"| 4.4 ||align=center style="background-color: #DDDDDD"| 460 ||align=center style="background-color: #DDDDDD"| 1470 years ||align=center style="background: {{star-color|B}}; | B1Vn ||align=center| 15.52 ||align=center| 1.8
|-
|align=center rowspan=2 style="background-color: #BBBBBB"| α<sup>1</sup> Crucis ||align=center style="background-color: #BBBBBB"| Acrux Aa ||align=center rowspan=2 style="background-color: #BBBBBB"| 0.0094 ||align=center rowspan=2 style="background-color: #BBBBBB"| 0.99 ||align=center rowspan=2 style="background-color: #BBBBBB"| 75.8 days ||align=center style="background: {{star-color|B}}; | B0.5IV ||align=center| 17.80 ||align=center rowspan=2|1.3<br />(combined)
|-
|align=center style="background-color: #BBBBBB"| Acrux ab ||align=center style="background: {{star-color|B}}; | B7?V ||align=center| 4.49
|}
{{reflist|group="orbit note"}}

== In culture ==

Acrux is represented in the flags of [[flag of Australia|Australia]], [[flag of New Zealand|New Zealand]], [[flag of Samoa|Samoa]], and [[flag of Papua New Guinea|Papua New Guinea]] as one of five stars that compose the [[Southern Cross]]. It is also featured in the [[flag of Brazil]], along with 26 other stars, each of which represents a state; Acrux represents the state of [[São Paulo (state)|São Paulo]].<ref>{{cite web
|title=Astronomy of the Brazilian Flag
|url=https://flagspot.net/flags/br_astro.html
|publisher=FOTW Flags Of The World website
}}</ref> As of 2015, it is also represented on the cover of the [[Brazilian passport]].

The Brazilian oceanographic research vessel [[Alpha Crucis (research vessel)|''Alpha Crucis'']] is named after the star.

== See also ==
* [[Lists of stars]]

== Notes ==
{{Notelist}}

== References ==
{{Reflist|30em|refs=

<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=GSM>{{citation | last=Perryman | first=Michael | title=The Making of History's Greatest Star Map | location=Heidelberg | publisher=Springer-Verlag | date=2010 | doi=10.1007/978-3-642-11602-5| series=Astronomers' Universe | isbn=978-3-642-11601-8 | bibcode=2010mhgs.book.....P | url=https://cds.cern.ch/record/1338896 | url-access=subscription }}</ref>

<ref name=houk1979>{{citation | title=Michigan catalogue of two-dimensional spectral types for the HD stars | journal=Ann Arbor: Dept. Of Astronomy | volume=1 | last1=Houk | first1=Nancy | date=1979 | bibcode=1978mcts.book.....H }}</ref>

<ref name=gcsrv53>{{cite journal | last=Wilson | first=Ralph Elmer | date=1953 | title=General Catalogue of Stellar Radial Velocities | journal=Carnegie Institute Washington D.C. Publication | bibcode=1953GCRV..C......0W }}</ref>

<ref name=lang2006>{{citation | first1=Kenneth R. | last1=Lang | title=Astrophysical formulae | volume=1 | series=Astronomy and astrophysics library | edition=3 | publisher=[[Birkhäuser]] | year=2006 | isbn=3-540-29692-1 | url=https://books.google.com/books?id=OvTjLcQ4MCQC&pg=PA41 }}. The radius (R<sub>*</sub>) is given by:
:<math>\begin{align} 2\cdot R_*
 & = \frac{(10^{-3}\cdot 99\cdot 0.52)\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\
 & 11.073\cdot R_{\bigodot}
\end{align}</math><br />The angular diameter used (0.52{{nbsp}}[[milliarcsecond]]s) is from [https://vizier.cds.unistra.fr/viz-bin/VizieR?-source=II/224&ID1=108249 CADARS]. Distance (99{{nbsp}}[[parsecs]]) is from Hipparcos.</ref>

<ref name=nomoto>{{cite journal|bibcode=1984ApJ...277..791N|title=Evolution of 8-10 solar mass stars toward electron capture supernovae. I - Formation of electron-degenerate O + NE + MG cores|journal=Astrophysical Journal|volume=277|pages=791|last1=Nomoto|first1=K.|year=1984|doi=10.1086/161749|doi-access=free}}</ref>
}}

==External links==
* http://jumk.de/astronomie/big-stars/acrux.shtml
* http://www.daviddarling.info/encyclopedia/A/Acrux.html

{{Stars of Crux}}
{{Portal bar|Astronomy|Stars|Outer space}}
{{Authority control}}
{{Sky|12|26|35.89522|-|63|05|56.7343}}

{{DEFAULTSORT:Acrux}}
<!-- Properties -->
[[Category:Double stars]]
[[Category:B-type main-sequence stars]]
[[Category:B-type subgiants]]
[[Category:Spectroscopic binaries]]
[[Category:Triple star systems]]
[[Category:Multiple star systems|6]]
[[Category:Lower Centaurus Crux]]
<!-- Location/catalogues -->
[[Category:Crux]]
[[Category:Bayer objects|Crucis, Alpha]]
[[Category:Bright Star Catalogue objects|4730 1]]
[[Category:Durchmusterung objects]]
[[Category:Hipparcos objects|060718]]
[[Category:Henry Draper Catalogue objects|108248 9]]
[[Category:Gould objects|Crucis, 26 7]]
[[Category:Stars with proper names|Acrux]]