AH Scorpii (abbreviated to AH Sco) is a red supergiant or hypergiant variable star located in the constellation Scorpius. It is one of the largest stars known by radius and is also one of the most luminous red supergiant stars in the Milky Way.
Observational history In 1907, Henrietta Swan Leavitt and Edward Charles Pickering announced the discovery of this variable star. It was given its variable star designation, AH Scorpii, in 1912. The total visual magnitude range is 6.5 - 9.6.
Distance Prior to the 21st century, the distance of AH Scorpii was considered to be uncertain, between about 1.5 and (kpc). VLBI measurements of the masers have provided an accurate distance of based on observation of , , and OH masers in its oxygen-rich circumstellar material. The masers were observed to be approaching the star at , indicating overall contraction at around phase 0.55 of the visual variations. Gaia Data Release 3 includes a parallax of , corresponding to a distance of about .
Characteristics The star is a dust-enshrouded red supergiant and is classified as a semiregular variable star with a main period of 714 days. No long secondary periods have been detected.
Modelling of AH Scorpii near maximum light has determined an effective temperature of and a luminosity of . A radius of was determined from an angular diameter of and the given distance of . Its angular diameter was re-measured at in 2023.
See also VY Canis Majoris NML Cygni KW Sagittarii UY Scuti
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