Delta Arae

Delta Arae, Latinized from δ Arae, is the Bayer designation for a double star in the southern constellation Ara. It has an apparent visual magnitude of 3.62 and is visible to the naked eye. Based upon an annual parallax of 16.48 mas, it is about 198 ly distant from the Earth.

Delta Arae is massive B-type main sequence star with a stellar classification of B8 Vn. The 'n' suffix indicates the absorption lines are spread out broadly because the star is spinning rapidly. It has a projected rotational velocity of 255 km/s, resulting in an equatorial bulge with a radius 13% larger than the polar radius. It has a magnitude 9.5 companion G-type main sequence star that may form a binary star system with Delta Arae.

There is a 12th magnitude optical companion located 47.4 arcseconds away along a position angle of 313°.

Etymology
Delta Arae was known as 龜三 (meaning: "the 3rd (star) of Guī") in traditional Chinese astronomy.

Allen erroneously called both Delta and Zeta Arae "Tseen Yin" (天陰). He probably confused the constellation "Ara" with "Ari", as 天陰 is actually in Aries.