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Beta Scorpii (β Scorpii, abbreviated Beta Sco, β Sco) is a multiple star system in the southern zodiac constellation of Scorpius. It bore the traditional proper name of Acrab Template:IPAc-en,<ref name=Rumrill>Template:Cite journal</ref> though the International Astronomical Union now regards that name as applying only to the β Scorpii Aa component.
ComponentsEdit
Observed through a small telescope, Beta Scorpii appears as a binary star with a separation between the two components of 13.5 arcseconds and a combined apparent magnitude of 2.50. This pair, designated β¹ Scorpii and β² Scorpii, form the top branches of a hierarchy of six orbiting components.
Template:Chart/start Template:Chart Template:Chart Template:Chart Template:Chart Template:Chart Template:Chart Template:Chart Template:Chart Template:Chart Template:Chart Template:Chart Template:Chart/end Hierarchy of orbits in the β Scorpii system
β¹ Scorpii, the brighter of the pair, consists of two sub-components, designated β Scorpii A and β Scorpii B, orbiting at an angular separation of 0.3 arcseconds with an orbital period of 610 years. β Scorpii A is itself a spectroscopic binary, with the two components designated β Scorpii Aa (also named Acrab<ref name="IAU-LSN"/>) and β Scorpii Ab. They are separated by 1.42 milliarcseconds and have an orbital period of 6.82 days.<ref name=aj140_3_735/>
β² Scorpii also has two sub-components, designated β Scorpii C and β Scorpii E, orbiting at an angular separation of 0.1328 arcseconds with an orbital period of 39 years. β Scorpii E in turn is a spectroscopic binary with components designated β Scorpii Ea and β Scorpii Eb and having an orbital period of 10.7 days.
Component β Scorpii D is the unrelated seventh magnitude star HD 144273, 520" away.<ref name=wds/> Some authors have also referred to component Ab as D.<ref name=vanflandern/>
A companion to component B, β Scorpii G, has been proposed to account for missing mass in the system, but no further evidence of its existence has been found.<ref name=catanzaro/> β Scorpii F refers to a theorised companion to component E.<ref name=vanflandern/>
NomenclatureEdit
β Scorpii (Latinised to Beta Scorpii) is the star's Bayer designation; β¹ and β² Scorpii, those of its two components. The designations of the sub-components - β Scorpii A, Aa, Ab, B, C, E, Ea and Eb - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).<ref name="planetnaming"/>
Beta Scorpii bore the traditional names Acrab, Akrab or Elacrab, all deriving from the Arabic name (Template:Langx) al-'Aqrab 'the Scorpion' for the whole constellation, as well as Graffias Template:IPAc-en,<ref name=Davis44>Template:Cite journal</ref> Italian for "the claws", a name it shared with Xi Scorpii.<ref name=graffias/><ref name=allen1899/>
In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)<ref name="WGSN"/> to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.<ref name="TriRpt18">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It approved the name Acrab for the component β Scorpii Aa on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.<ref name="IAU-LSN"/>
In Chinese, {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), meaning Room, refers to an asterism consisting of both of β1 Scorpii and β2 Scorpii, π Scorpii, ρ Scorpii and δ Scorpii, .<ref>Template:In lang 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, Template:ISBN.</ref> Consequently, the Chinese name for both of β1 Scorpii and β2 Scorpii is {{#invoke:Lang|lang}} ({{#invoke:Lang|lang}}), "the Fourth Star of Room".<ref>Template:In lang 香港太空館 - 研究資源 - 亮星中英對照表 Template:Webarchive, Hong Kong Space Museum. Accessed on line November 23, 2010.</ref>
NamesakeEdit
USS Graffias (AF-29) was once a United States navy ship named after the star.
PropertiesEdit
The β Scorpii system is a kinematic member of the Upper Scorpius subgroup of the Scorpius–Centaurus association, a group of thousands of young stars with mean age 11 million years at distance 470 light years (145 parsecs). Analysis of β1 Scorpii as a single star derived an evolutionary age between 9 and 12 million years,<ref name="Pecaut"/> but analysis of the β Scorpii system as a whole suggest an age closer to 6 million years.<ref name=catanzaro/>
The two components of β Scorpii A are the most massive members of the system, Template:Solar mass and Template:Solar mass respectively. The combined spectral type is B1 V. The individual spectral types cannot be clearly measured, but are estimated to be B0.5 and B1.5. Component Aa is evolving slightly away from the zero age main sequence and its luminosity class is estimated to be intermediate between subgiant (IV) and main sequence (V). Component Ab has a main sequence luminosity class, a temperature of 26,400 K, and a luminosity of Template:Solar luminosity.
Component B is over 20 times fainter than the combined component A stars and a clear spectral type has not been measured. Its mass is estimated to be approximately Template:Solar mass.<ref name=vanflandern/>
Component C has a stellar classification of B2 V and a mass of Template:Solar mass. It has an effective surface temperature of 24,000 K, a radius of Template:Solar radius and a bolometric luminosity of Template:Solar luminosity.
Component E is determined to have a temperature of 13,000 K, radius of Template:Solar radius, and luminosity of Template:Solar luminosity. It is chemically peculiar, with high abundances of manganese and strontium. It is possibly a mercury-manganese (HgMn) star, but abundances of other metals are unexpectedly low.<ref name=catanzaro/>
Beta Scorpii is 1.01 degree from the ecliptic and can be occulted by the Moon and, very rarely, by planets. On December 9, 1906, it was occulted by Venus.<ref name=Koennen1981/> The last occultation by a planet took place on 13 May 1971, by Jupiter.<ref>Template:Cite journal </ref>
ObservationEdit
On 11 December 2019, it had a close conjunction (geocentric separation <1') with Mercury.<ref name="Mus2002">Template:Cite book</ref>Template:Rp
In cultureEdit
Beta Scorpii appears on the flag of Brazil, symbolising the state of Maranhão.<ref name=abf/>