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Acrux

Coordinates:Sky map12h26m35.89522s,−63° 05′ 56.7343″
From Wikipedia, the free encyclopedia
This article is about the star. For the Christian college, seeAlphacrucis.For research ship, seeAlpha Crucis (research vessel).
Acrux

The position of Acrux
Observation data
EpochJ2000EquinoxJ2000
Constellation Crux
Pronunciation /ˈeɪkrʌks/[citation needed]
Right ascension 12h26m35.89522s[1]
Declination −63° 05′ 56.7343″[1]
Apparent magnitude(V) 0.76[2](1.33 + 1.75)[3]
Characteristics
Spectral type B0.5IV + B1V[4]
B−Vcolor index −0.26[2]
Variable type β Cep[5]
Astrometry
Radial velocity(Rv)−11.2 / −0.6[6]km/s
Proper motion(μ)RA:−35.83[1]mas/yr
Dec.:−14.86[1]mas/yr
Parallax(π)10.13 ± 0.50mas[1]
Distance320 ± 20ly
(99 ± 5pc)
Absolute magnitude(MV)−3.77[7](−2.2 + −2.7[8])
Orbit[9]
Primaryα Crucis Aa
Companionα Crucis Ab
Period(P)75.7794±0.0037 d
Eccentricity(e)0.46±0.03
Periastronepoch(T)2,417,642.3±1.6 JD
Argument of periastron(ω)
(secondary)		21±6°
Semi-amplitude(K1)
(primary)		41.7±1.2km/s
Details
α1
Mass17.80 + 6.05[3]M☉
Radius7.29 ± 0.34[5][a]R☉
Luminosity31,110+3,190
−2,910[5]L☉
Temperature28,840[5]K
Rotational velocity(vsini)124[5]km/s
α2
Mass15.52[3]M☉
Radius5.53[10]R☉
Luminosity16,000[11]L☉
Temperature28,000[12]K
Rotational velocity(vsini)200[12]km/s
Age10.8[13]Myr
Other designations
α Crucis,CPD−62°2745,HIP60718,CCDMJ12266-6306,WDSJ12266-6306
α1Cru:Acrux,26 G.Crucis,FK5462,GC16952,HD108248,HR4730
α2Cru:27 G.Crucis,GC16953,HD108249,HR4731,2MASSJ12263615-6305571
Database references
SIMBADα Cru
α1Cru
α2Cru

Acruxis the brighteststarin the southernconstellationofCrux.It has theBayer designationα Crucis,which isLatinisedtoAlpha Crucisand abbreviatedAlpha Cruorα Cru.With a combinedvisual magnitudeof +0.76, it is the13th-brightest starin thenight sky.It is the most southerly star of theasterismknown as the Southern Cross and is the southernmostfirst-magnitude star,2.3 degrees more southerly thanAlpha Centauri.[14]This system is located at a distance of 321light-yearsfrom theSun.[1][15]

To the naked eye Acrux appears as a single star, but it is actually a multiple star system containing six components. Through opticaltelescopes,Acrux appears as atriple star,whose two brightest components are visually separated by about 4arcsecondsand are known as Acrux A and Acrux B, α1Crucis and α2Crucis, or α Crucis A and α Crucis B. Both components areB-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 aJesuit priest.[16]α1Crucis is itself aspectroscopic binarywith components designated α Crucis Aa (officially namedAcrux,historically the name of the entire system)[17][18]and α Crucis Ab. Its two component stars orbit every 76 days at a separation of about 1astronomical unit(AU).[11]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[edit]

The constellationCrux

α Crucis(Latinised toAlpha Crucis) is the system'sBayer designation;α1andα2Crucis,those of its two main components stars. The designations of these two constituents asAcrux AandAcrux Band those ofA'scomponents—Acrux AaandAcrux Ab—derive from the convention used by theWashington Multiplicity Catalog(WMC) for multiple star systems,[dubious–discuss]and adopted by theInternational Astronomical Union(IAU).[19][unreliable source?]

The historical nameAcruxforα1Crucisis an "Americanism"coined in the 19th century, but entering common use only by the mid 20th century.[20][better source needed]In 2016, theInternational Astronomical Unionorganized aWorking Group on Star Names(WGSN)[21]to catalog and standardize proper names for stars. The WGSN states that in the case ofmultiple starsthe name should be understood to be attributed to the brightest component by visual brightness.[22]The WGSN approved the nameAcruxfor the starAcrux Aaon 20 July 2016 and it is now so entered in the IAU Catalog of Star Names.[18]

Since Acrux is at −63°declination,making it the southernmost first-magnitude star, it is only visible south oflatitude27° North. It barely rises from cities such asMiami,United States,orKarachi,Pakistan(both around 25°N) and not at all fromNew Orleans,United States,orCairo,Egypt(both about 30°N). Because of Earth'saxial precession,the star was visible to ancientHinduastronomers inIndiawho named itTri-shanku.It was also visible to theancient RomansandGreeks,who regarded it as part of the constellation ofCentaurus.[23]

InChinese,Thập tự giá(Shí Zì Jià,"Cross"), refers to an asterism consisting of Acrux,Mimosa,Gamma CrucisandDelta Crucis.[24]Consequently, Acrux itself is known asThập tự giá nhị(Shí Zì Jià èr,"the Second Star of Cross" ).[25]

This star is known asEstrela de Magalhães( "Star ofMagellan") inPortuguese.[26]

Stellar properties[edit]

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

The two components, α1and α2Crucis, are separated by 4arcseconds.α1is magnitude 1.40 and α2is magnitude 2.09, both earlyclass Bstars, with surface temperatures of about 28,000 and26,000K,respectively. Their luminosities are 25,000 and 16,000 timesthat of the Sun.α1and α2orbit 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.[3]

α1is itself a spectroscopicbinary star,with its components thought to be around 14 and 10 times themass of the Sunand orbiting in only 76 days at a separation of about1AU.The masses of α2and the brighter component α1suggest that the stars will someday explode assupernovae.[11]Component Ab may perform electron capture in the degenerate O+Ne+Mg core and trigger a supernova explosion,[27][28]otherwise it will become a massive white dwarf.[11]

Photometry with theTESSsatellite has shown that one of the stars in the α Crucis system is aβ Cephei variable,although α1and α2Crucis are too close for TESS to resolve and determine which one is the pulsator.[5]

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 theScorpius–Centaurus association.It was not previously seen to be a member of the group.[29]

The cooler, less-luminous B-class starHR 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.[30][31]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.[32]

On 2 October 2008, theCassini–Huygensspacecraft resolved three of the components (A, B and C) of the multiple star system asSaturn's disk occulted it.[33][34]

Acrux system
Separation
(arcsec) 		Projected
separation
(AU) 		Orbital
period 		Spectral
type 		Mass
(M☉) 		App. mag.
(V)
Acrux ABC HR 4729ABC
(Acrux C & CP)
[orbit note 1]		 α1Crucis 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
(α1and α2)
[orbit note 1]		 α2Crucis 4.4 460 1470 years B1Vn 15.52 1.8
α1Crucis Acrux Aa 0.0094 0.99 75.8 days B0.5IV 17.80 1.3
(combined)
Acrux ab B7?V 4.49
  1. ^abHR 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[edit]

Acrux is represented in the flags ofAustralia,New Zealand,Samoa,andPapua New Guineaas one of five stars that compose theSouthern Cross.It is also featured in theflag of Brazil,along with 26 other stars, each of which represents a state; Acrux represents the state ofSão Paulo.[35]As of 2015, it is also represented on the cover of theBrazilian passport.

The Brazilian oceanographic research vesselAlpha Crucisis named after the star.

See also[edit]

Notes[edit]

  1. ^Applying theStefan–Boltzmann lawwith a nominalsolareffective temperatureof 5,772K:
    .

References[edit]

  1. ^abcdefvan 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,S2CID18759600
  2. ^abCorben, 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. ^abcdTokovinin, 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.ISSN0365-0138.
  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. ^abcdefSharma, 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.S2CID54222753.
  8. ^Van De Kamp, Peter (1953)."The Twenty Brightest Stars".Publications of the Astronomical Society of the Pacific.65(382): 30.Bibcode:1953PASP...65...30V.doi:10.1086/126523.
  9. ^Thackeray, A. D.; Wegner, G. (April 1980), "An improved spectroscopic orbit for α1Crucis ",Monthly Notices of the Royal Astronomical Society,191(2): 217–220,Bibcode:1980MNRAS.191..217T,doi:10.1093/mnras/191.2.217
  10. ^Lang, Kenneth R. (2006),Astrophysical formulae,Astronomy and astrophysics library, vol. 1 (3 ed.),Birkhäuser,ISBN3-540-29692-1.The radius (R*) is given by:

    The angular diameter used (0.52milliarcseconds) is fromCADARS.Distance (99parsecs) is from Hipparcos.
  11. ^abcdKaler, James B. (2002). "Acrux".The Hundred Greatest Stars.pp. 4–5.doi:10.1007/0-387-21625-1_2.ISBN978-0-387-95436-3.
  12. ^abDravins, Dainis; Jensen, Hannes; Lebohec, Stephan; Nuñez, Paul D. (2010). "Stellar intensity interferometry: Astrophysical targets for sub-milliarcsecond imaging".Proceedings of the SPIE.Optical and Infrared Interferometry II.7734:77340A.arXiv:1009.5815.Bibcode:2010SPIE.7734E..0AD.doi:10.1117/12.856394.S2CID55641060.
  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.S2CID118629873.
  14. ^Bordeleau, André G. (12 August 2013). "Federative Republic of Brazil: Constellations in the Breeze".Flags of the Night Sky.New York: Springer. pp. 1–72.doi:10.1007/978-1-4614-0929-8_1.ISBN978-1-4614-0928-1.
  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,ISBN978-3-642-11601-8
  16. ^https://cfah.org.za/outreach/crux/
  17. ^Kunitzsch, Paul; Smart, Tim (2006).A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations(2nd rev. ed.). Cambridge, Massachusetts: Sky Pub.ISBN978-1-931559-44-7.
  18. ^ab"IAU Catalog of Star Names".Retrieved21 November2016.
  19. ^Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets".arXiv:1012.0707[astro-ph.SR].
  20. ^Memoirs of the Rev. Walter M. Lowrie: missionary to China(1849), p. 93. Described as an "Americanism" inThe Geographical Journal,vol. 92, Royal Geographical Society, 1938.
  21. ^"IAU Working Group on Star Names (WGSN)".Retrieved22 May2016.
  22. ^"Bulletin of the IAU Working Group on Star Names, No. 2"(PDF).Retrieved12 October2016.
  23. ^Richard Hinckley Allen,Star Names: Their Lore and Meaning,Dover Books, 1963.
  24. ^(in Chinese)Trung quốc tinh tọa thần thoại,written by trần cửu kim. Published by đài loan thư phòng xuất bản hữu hạn công tư, 2005,ISBN978-986-7332-25-7.
  25. ^(in Chinese)Hương cảng thái không quán - nghiên cứu tư nguyên - lượng tinh trung anh đối chiếu biểuArchived2010-09-03 at theWayback Machine,Hong Kong Space Museum. Accessed on line November 23, 2010.
  26. ^Silva, Guilherme Marques dos Santos; Ribas, Felipe Braga; Freitas, Mário Sérgio Teixeira de (2008)."Transformação de coordenadas aplicada à construção da maquete tridimensional de uma constelação".Revista Brasileira de Ensino de Física.30:1306.1–1306.7.doi:10.1590/S1806-11172008000100007.
  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.S2CID119163256.
  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,S2CID54510608.
  30. ^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.S2CID16697655.
  31. ^Eggleton, Peter; Tokovinin, A. (2008). "A catalogue of multiplicity among bright stellar systems".Monthly Notices of the Royal Astronomical Society.389(2): 869–879.arXiv:0806.2878.Bibcode:2008MNRAS.389..869E.doi:10.1111/j.1365-2966.2008.13596.x.S2CID14878976.
  32. ^Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001)."The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog".The Astronomical Journal.122(6): 3466–3471.Bibcode:2001AJ....122.3466M.doi:10.1086/323920.
  33. ^"Cassini raw image".NASA/JPL/Space Science Institute.Retrieved2017-10-31.
  34. ^Cassini "Kodak Moments" - Unmanned Spaceflight.com.Retrieved 2008-10-21
  35. ^"Astronomy of the Brazilian Flag".FOTW Flags Of The World website.

External links[edit]


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