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}} }}
{{Starbox observe {{Starbox observe
| pronounce= {{IPAc-en|'|ei|k|r|V|k|s}}{{cn|date=May 2022}} | pronounce= {{IPAc-en|'|ei|k|r|V|k|s}}{{citation needed|date=May 2022}}
| epoch = J2000 | epoch = J2000
| constell = ] | constell = ]
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| b-v = −0.26<ref name=corben/> | b-v = −0.26<ref name=corben/>
| u-b = | u-b =
| variable = ]<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>
| variable =
}} }}
{{Starbox astrometry {{Starbox astrometry
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| journal=Monthly Notices of the Royal Astronomical Society | journal=Monthly Notices of the Royal Astronomical Society
| volume=191 | issue=2 | pages=217–220 | date=April 1980 | 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> | doi=10.1093/mnras/191.2.217 | bibcode=1980MNRAS.191..217T| doi-access= free}}</ref>
| name=α Crucis Ab | name=α Crucis Ab
| period_unitless = {{Val|75.7794|0.0037|u=day}} | period_unitless = {{Val|75.7794|0.0037|u=day}}
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| metal_fe = | metal_fe =
| mass = 17.80 + 6.05<ref name="Tokovinin1997"/> | 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 ] with a nominal ] ] of 5,772&nbsp;]:
| radius = 7.8<ref>{{Cite web|url=https://www.wolframalpha.com/input/?i=acrux+luminosity|title=Acrux luminosity - Wolfram{{pipe}}Alpha}}</ref>
:<math>\sqrt{\biggl(\frac{5,772}{28,840}\biggr)^4 \cdot 10^{4.52}} = 7.289\ R_\odot</math>.}}
| rotation = | rotation =
| luminosity = 25,000<ref name=kaler/> | luminosity = {{val|31,110|3190|2910|fmt=commas}}<ref name=Sharma/>
| rotational_velocity = 120<ref name=dravins/> | rotational_velocity = 124<ref name=Sharma/>
| temperature = 28,840<ref name=Sharma/>
⚫ | temperature = 24,000<ref name=dravins>{{cite journal|bibcode=2010SPIE.7734E..0AD|arxiv=1009.5815|title=Stellar intensity interferometry: Astrophysical targets for sub-milliarcsecond imaging|journal=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.|year=2010|doi=10.1117/12.856394|series=Optical and Infrared Interferometry II|s2cid=55641060}}</ref>
| component2 = α<sup>2</sup> | component2 = α<sup>2</sup>
| metal_fe2 = | metal_fe2 =
| mass2 = 15.52<ref name="Tokovinin1997"/> | mass2 = 15.52<ref name="Tokovinin1997"/>
| radius2 = {{solar radius calculator|type=AD|0.52|0.099|decimals=2}}<ref name=lang2006/>
| radius2 = 5.4
| luminosity2 = 16,000<ref name=kaler/> | 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>
| rotational_velocity2 = 200<ref name=dravins/>
| temperature2 = 28,000<ref name=dravins/> | 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|arxiv = 1007.4883 |s2cid= 118629873}}</ref> | 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 {{Starbox catalog
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{{Starbox end}} {{Starbox end}}


'''Acrux''' is the brightest ] in the southern ] of ]. It has the ] '''α Crucis''', which is ] to '''Alpha Crucis''' and abbreviated '''Alpha Cru''' or '''α Cru'''. With a combined ] of +0.76, it is the ] in the ].<!-- 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 ] known as the Southern Cross and is the southernmost ], 2.3 degrees more southerly than ].<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 ]s from the ].<ref name=aaa474_2_653/><ref name=GSM/> '''Acrux''' is the brightest ] in the southern ] of ]. It has the ] '''α Crucis''', which is ] to '''Alpha Crucis''' and abbreviated '''Alpha Cru''' or '''α Cru'''. With a combined ] of +0.76, it is the ] in the ].<!-- 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 ] known as the Southern Cross and is the southernmost ], 2.3 degrees more southerly than ].<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 ]s from the ].<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 ]s, Acrux appears as a ], whose two brightest components are visually separated by about 4 ]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 ]s, and are many times more massive and luminous than the Sun. α<sup>1</sup> Crucis is itself a ] with components designated α Crucis Aa (officially named '''Acrux''', historically the name of the entire system)<ref name=Kunitzsch>{{cite book To the naked eye Acrux appears as a single star, but it is actually a multiple star system containing six components. Through optical ]s, Acrux appears as a ], whose two brightest components are visually separated by about 4 ]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 ]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 ].<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 ] 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 |last1=Kunitzsch |first1=Paul
|last2=Smart |first2=Tim |last2=Smart |first2=Tim
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==Stellar properties== ==Stellar properties==
]]] ] (the 2nd-brightest star)]]
The two components, α<sup>1</sup> and α<sup>2</sup> Crucis, are separated by 4 ]. α<sup>1</sup> is magnitude 1.40 and α<sup>2</sup> is magnitude 2.09, both early ] 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 ]. 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"/> The two components, α<sup>1</sup> and α<sup>2</sup> Crucis, are separated by 4 ]. α<sup>1</sup> is magnitude 1.40 and α<sup>2</sup> is magnitude 2.09, both early ] 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 ]. 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 ], with its components thought to be around 14 and 10 times the ] 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 α<sup>1</sup> suggest that the stars will someday explode as ]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 |url=https://arxiv.org/abs/1505.06712#:~:text=The%20post%2Dhelium%20burning%20evolution,standard%20set%20of%20stellar%20physics. |access-date=February 5, 2022}}</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> α<sup>1</sup> is itself a spectroscopic ], with its components thought to be around 14 and 10 times the ] 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 ] and ] (similar to ] and ]) before exploding as ]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 ] satellite has shown that one of the stars in the α Crucis system is a ], 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 ]. 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 | bibcode=2011MNRAS.416.3108R | arxiv=1106.2857 | s2cid=54510608 | postscript=. }}</ref>


⚫ 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 ]. 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 ] is present around α Crucis, and is visible in the ] 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 ] (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=]|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 |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>

⚫ The cooler, less-luminous B-class star ] (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=]|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 ] spacecraft resolved three of the components (A, B and C) of the multiple star system as ]'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|access-date=2017-10-31 }}</ref><ref>. Retrieved 2008-10-21</ref> On 2 October 2008, the ] spacecraft resolved three of the components (A, B and C) of the multiple star system as ]'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|access-date=2017-10-31 }}</ref><ref>. Retrieved 2008-10-21</ref>

{|class="wikitable"
|+Acrux system
!colspan=4|
!Separation<br />(])
!Projected<br />separation<br />(])
!Orbital<br />period
!]
!Mass<br />(])
!]<br />(V)
|-
|align=center rowspan=6| Acrux ABC ||align=center rowspan=3 style="background-color: #EEEEEE"| ] 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 == == In culture ==


Acrux is represented in the flags of ], ], ] and ] as one of five stars which comprise the ]. It is also featured in the ], along with 26 other stars, each of which represents a state; Acrux representing the state of ].<ref>{{cite web Acrux is represented in the flags of ], ], ], and ] as one of five stars that compose the ]. It is also featured in the ], along with 26 other stars, each of which represents a state; Acrux represents the state of ].<ref>{{cite web
|title=Astronomy of the Brazilian Flag |title=Astronomy of the Brazilian Flag
|url=https://flagspot.net/flags/br_astro.html |url=https://flagspot.net/flags/br_astro.html
|publisher=FOTW Flags Of The World website |publisher=FOTW Flags Of The World website
}}</ref> It is also represented (as part of the Southern Cross) on the cover of the current (from 2015) ]. }}</ref> As of 2015, it is also represented on the cover of the ].


The Brazilian oceanographic research vessel ] is named after the star. The Brazilian oceanographic research vessel ] is named after the star.
Line 125: Line 152:
== See also == == See also ==
* ] * ]

== Notes ==
{{Notelist}}


== References == == References ==
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<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=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 | journal=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=http://cds.cern.ch/record/1338896 }}</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 }}</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=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=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=] | 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:
⚫ <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}}</ref>
:<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}}]s) is from . Distance (99{{nbsp}}]) 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>
}} }}


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Latest revision as of 23:55, 12 November 2024

Star in the constellation Crux This article is about the star. For the Christian college, see Alphacrucis. For research ship, see Alpha Crucis (research vessel).
Acrux

The position of Acrux
Observation data
Epoch J2000      Equinox J2000
Constellation Crux
Pronunciation /ˈeɪkrʌks/
Right ascension 12 26 35.89522
Declination −63° 05′ 56.7343″
Apparent magnitude (V) 0.76 (1.33 + 1.75)
Characteristics
Spectral type B0.5IV + B1V
B−V color index −0.26
Variable type β Cep
Astrometry
Radial velocity (Rv)−11.2 / −0.6 km/s
Proper motion (μ) RA: −35.83 mas/yr
Dec.: −14.86 mas/yr
Parallax (π)10.13 ± 0.50 mas
Distance320 ± 20 ly
(99 ± 5 pc)
Absolute magnitude (MV)−3.77 (−2.2 + −2.7)
Orbit
Primaryα Crucis Aa
Companionα Crucis Ab
Period (P)75.7794±0.0037 d
Eccentricity (e)0.46±0.03
Periastron epoch (T)2,417,642.3±1.6 JD
Argument of periastron (ω)
(secondary)		21±6°
Semi-amplitude (K1)
(primary)		41.7±1.2 km/s
Details
α
Mass17.80 + 6.05 M☉
Radius7.29 ± 0.34 R☉
Luminosity31,110+3,190
−2,910 L☉
Temperature28,840 K
Rotational velocity (v sin i)124 km/s
α
Mass15.52 M☉
Radius5.53 R☉
Luminosity16,000 L☉
Temperature28,000 K
Rotational velocity (v sin i)200 km/s
Age10.8 Myr
Other designations
α Crucis, CPD−62°2745, HIP 60718, CCDM J12266-6306, WDS J12266-6306
α Cru: Acrux, 26 G. Crucis, FK5 462, GC 16952, HD 108248, HR 4730
α Cru: 27 G. Crucis, GC 16953, HD 108249, HR 4731, 2MASS J12263615-6305571
Database references
SIMBADα Cru
α Cru
α Cru

Acrux is the brightest star in the southern constellation of Crux. It has the Bayer designation α Crucis, which is Latinised to Alpha Crucis and abbreviated Alpha Cru or α Cru. With a combined visual magnitude of +0.76, it is the 13th-brightest star in the night sky. It is the most southerly star of the asterism known as the Southern Cross and is the southernmost first-magnitude star, 2.3 degrees more southerly than Alpha Centauri. This system is located at a distance of 321 light-years from the Sun.

To the naked eye Acrux appears as a single star, but it is actually a multiple star system containing six components. Through optical telescopes, Acrux appears as a triple star, whose two brightest components are visually separated by about 4 arcseconds and are known as Acrux A and Acrux B, α Crucis and α Crucis, or α Crucis A and α Crucis B. Both components are B-type stars, 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. α Crucis is itself a spectroscopic binary with components designated α Crucis Aa (officially named Acrux, historically the name of the entire system) and α Crucis Ab. Its two component stars orbit every 76 days at a separation of about 1 astronomical unit (AU). 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

The constellation Crux

α Crucis (Latinised to Alpha Crucis) is the system's Bayer designation; α and α 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, and adopted by the International Astronomical Union (IAU).

The historical name Acrux for α Crucis is an "Americanism" coined in the 19th century, but entering common use only by the mid 20th century. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN states that in the case of multiple stars the name should be understood to be attributed to the brightest component by visual brightness. 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.

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 Greeks, who regarded it as part of the constellation of Centaurus.

In Chinese, 十字架 (Shí Zì Jià, "Cross"), refers to an asterism consisting of Acrux, Mimosa, Gamma Crucis and Delta Crucis. Consequently, Acrux itself is known as 十字架二 (Shí Zì Jià èr, "the Second Star of Cross").

This star is known as Estrela de Magalhães ("Star of Magellan") in Portuguese.

Stellar properties

α Crucis with the nearby HD 108250 (the 2nd-brightest star)

The two components, α and α Crucis, are separated by 4 arcseconds. α is magnitude 1.40 and α is magnitude 2.09, both early class B stars, with surface temperatures of about 28,000 and 26,000 K, respectively. Their luminosities are 25,000 and 16,000 times that of the Sun. α and α 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.

α 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 1 AU. The masses of α and the brighter component of α suggest that the stars will someday expand into blue and red supergiants (similar to Betelgeuse and Antares) before exploding as supernovae. Component Ab may perform electron capture in the degenerate O+Ne+Mg core and trigger a supernova explosion, otherwise it will become a massive white dwarf.

Photometry with the TESS satellite has shown that one of the stars in the α Crucis system is a β Cephei variable, although α and α Crucis are too close for TESS to resolve and determine which one is the pulsator.

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. 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.

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. 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.

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.

Acrux system
Separation
(arcsec) 		Projected
separation
(AU) 		Orbital
period 		Spectral
type 		Mass
(M☉) 		App. mag.
(V)
Acrux ABC HR 4729 ABC
(Acrux C & CP)
 α Crucis CP 2.1 220 930 years M0V 0.47 15.0
HR 4729 AB HR 4729 A 0.00046 0.048 1.225 days B4V 8.68 4.9
(combined)
HR 4729 B G?V 0.97
Acrux AB
(α and α)
 α Crucis 4.4 460 1470 years B1Vn 15.52 1.8
α Crucis Acrux Aa 0.0094 0.99 75.8 days B0.5IV 17.80 1.3
(combined)
Acrux ab B7?V 4.49
  1. ^ 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.

In culture

Acrux is represented in the flags of Australia, New Zealand, Samoa, and 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. As of 2015, it is also represented on the cover of the Brazilian passport.

The Brazilian oceanographic research vessel Alpha Crucis is named after the star.

See also

Notes

  1. Applying the Stefan–Boltzmann law with a nominal solar effective temperature of 5,772 K:
    ( 5 , 772 28 , 840 ) 4 ⋅ 10 4.52 = 7.289   R ⊙ {\displaystyle {\sqrt {{\biggl (}{\frac {5,772}{28,840}}{\biggr )}^{4}\cdot 10^{4.52}}}=7.289\ R_{\odot }} .

References

  1. ^ van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357, S2CID 18759600
  2. ^ Corben, P. M. (1966). "Photoelectric magnitudes and colours for bright southern stars". Monthly Notes of the Astron. Soc. Southern Africa. 25: 44. Bibcode:1966MNSSA..25...44C.
  3. ^ Tokovinin, A. A. (1997). "MSC - a catalogue of physical multiple stars". Astronomy and Astrophysics Supplement Series. 124 (1): 75–84. Bibcode:1997A&AS..124...75T. doi:10.1051/aas:1997181. ISSN 0365-0138.
  4. Houk, Nancy (1979), "Michigan catalogue of two-dimensional spectral types for the HD stars", Ann Arbor: Dept. Of Astronomy, 1, Bibcode:1978mcts.book.....H
  5. ^ Sharma, Awshesh N.; Bedding, Timothy R.; Saio, Hideyuki; White, Timothy R. (2022). "Pulsating B stars in the Scorpius–Centaurus Association with TESS". Monthly Notices of the Royal Astronomical Society. 515 (1): 828–840. arXiv:2203.02582. Bibcode:2022MNRAS.515..828S. doi:10.1093/mnras/stac1816.
  6. Wilson, Ralph Elmer (1953). "General Catalogue of Stellar Radial Velocities". Carnegie Institute Washington D.C. Publication. Bibcode:1953GCRV..C......0W.
  7. Kaltcheva, N. T.; Golev, V. K.; Moran, K. (2014). "Massive stellar content of the Galactic supershell GSH 305+01-24". Astronomy & Astrophysics. 562: A69. arXiv:1312.5592. Bibcode:2014A&A...562A..69K. doi:10.1051/0004-6361/201321454. S2CID 54222753.
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  10. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
    2 ⋅ R ∗ = ( 10 − 3 ⋅ 99 ⋅ 0.52 )   AU 0.0046491   AU / R ⨀ 11.073 ⋅ R ⨀ {\displaystyle {\begin{aligned}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{aligned}}}
    The angular diameter used (0.52 milliarcseconds) is from CADARS. Distance (99 parsecs) is from Hipparcos.
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  13. Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society. 410 (1): 190–200. arXiv:1007.4883. Bibcode:2011MNRAS.410..190T. doi:10.1111/j.1365-2966.2010.17434.x. S2CID 118629873.
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  15. Perryman, Michael (2010), The Making of History's Greatest Star Map, Astronomers' Universe, Heidelberg: Springer-Verlag, Bibcode:2010mhgs.book.....P, doi:10.1007/978-3-642-11602-5, ISBN 978-3-642-11601-8
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  27. Nomoto, K. (1984). "Evolution of 8-10 solar mass stars toward electron capture supernovae. I - Formation of electron-degenerate O + NE + MG cores". Astrophysical Journal. 277: 791. Bibcode:1984ApJ...277..791N. doi:10.1086/161749.
  28. S. E. Woosley, Alexander Heger (May 25, 2015). "The Remarkable Deaths of 9 - 11 Solar Mass Stars". Astrophysics. 810 (1): 34. arXiv:1505.06712. Bibcode:2015ApJ...810...34W. doi:10.1088/0004-637X/810/1/34. S2CID 119163256.
  29. Rizzuto, Aaron; Ireland, Michael; Robertson, J. G. (October 2011), "Multidimensional Bayesian membership analysis of the Sco OB2 moving group", Monthly Notices of the Royal Astronomical Society, 416 (4): 3108–3117, arXiv:1106.2857, Bibcode:2011MNRAS.416.3108R, doi:10.1111/j.1365-2966.2011.19256.x, S2CID 54510608.
  30. Torosyan, M.; Azatyan, N.; Nikoghosyan, E.; Samsonyan, A.; Andreasyan, D. (2024). "The runaway nature and origin of α Crucis system". Communications of the Byurakan Astrophysical Observatory. 71: 42–47. arXiv:2407.09934. Bibcode:2024CoBAO..71...42T. doi:10.52526/25792776-24.71.1-42.
  31. Shatsky, N.; Tokovinin, A. (2002). "The mass ratio distribution of B-type visual binaries in the Sco OB2 association". Astronomy and Astrophysics. 382: 92–103. arXiv:astro-ph/0109456. Bibcode:2002A&A...382...92S. doi:10.1051/0004-6361:20011542. S2CID 16697655.
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