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Beta Scorpii

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Beta Scorpii is a multiple star system in the southern zodiac constellation of Scorpius. It bore the traditional proper name of Acrab Template:IPAc-en,[1] though the International Astronomical Union now regards that name as applying only to the β Scorpii Aa component.

Components

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.

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[2]) and β Scorpii Ab. They are separated by 1.42 milliarcseconds and have an orbital period of 6.82 days.[3]

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.[4] Some authors have also referred to component Ab as D.[5]

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.[6] β Scorpii F refers to a theorised companion to component E.[5]

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Nomenclature

Beta Scorpii is the star's Bayer designation. This designation is Latinized from β Scorpii, and abbreviated Beta Sco or β Sco. β1 and β2 Scorpii are 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).[7]

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,[8] Italian for "the claws", a name it shared with Xi Scorpii.[9][10]

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[11] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[12] 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.[2]

In Chinese, Script error: No such module "Lang". (Script error: No such module "Lang".), meaning Room, refers to an asterism consisting of both of β1 Scorpii and β2 Scorpii, π Scorpii, ρ Scorpii and δ Scorpii, .[13] Consequently, the Chinese name for both of β1 Scorpii and β2 Scorpii is Script error: No such module "Lang". (Script error: No such module "Lang".), "the Fourth Star of Room".[14]

Namesake

USS Graffias (AF-29) was once a United States navy ship named after the star.

Properties

File:Guisard - Milky Way.jpg
Image of Scorpius and the Milky Way with β Scorpii in the top right corner

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,[15] but analysis of the β Scorpii system as a whole suggest an age closer to 6 million years.[6]

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.[5]

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.[6]

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.[16] The last occultation by a planet took place on 13 May 1971, by Jupiter.[17]

Observation

On 11 December 2019, it had a close conjunction (geocentric separation <1') with Mercury.[18]Template:Rp

In culture

Beta Scorpii appears on the flag of Brazil, symbolising the state of Maranhão.[19]

References

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Template:Stars of Scorpius

β Scorpii
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Location of β Scorpii (circled)
  1. ↑ Template:Cite journal
  2. ↑ a b Cite error: Invalid <ref> tag; no text was provided for refs named IAU-LSN
  3. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named aj140_3_735
  4. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named wds
  5. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named vanflandern
  6. ↑ a b c Cite error: Invalid <ref> tag; no text was provided for refs named catanzaro
  7. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named planetnaming
  8. ↑ Template:Cite journal
  9. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named graffias
  10. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named allen1899
  11. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named WGSN
  12. ↑ Script error: No such module "citation/CS1".
  13. ↑ 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.
  14. ↑ 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.
  15. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Pecaut
  16. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Koennen1981
  17. ↑ Template:Cite journal
  18. ↑ Script error: No such module "citation/CS1".
  19. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named abf
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