Acrab

TBC

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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 /ˈækræb/,^[8] though the International Astronomical Union now regards that name as applying only to the β Scorpii Aa component.

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^[9]) and β Scorpii Ab. They are separated by 1.42 milliarcseconds and have an orbital period of 6.82 days.^[10]

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.^[11] Some authors have also referred to component Ab as D.^[12]

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.^[7] β Scorpii F refers to a theorised companion to component E.^[12]