Alpha Arae

Alpha Arae (α Arae, α Ara) is the second brightest star in the southern constellation of Ara. With an average apparent visual magnitude 2.93, it is readily visible to the naked eye from the southern hemisphere. This star is close enough to the Earth that its distance can be estimated using parallax data collected during the Hipparcos mission. It is around 270 light-years (83 parsecs) away, with a 7% margin of error. The visual magnitude of the star is diminished by 0.10 magnitudes as a result of extinction from intervening gas and dust.

Properties

Alpha Arae has a stellar classification of B2 Vne, indicating that it is a massive B-type main sequence star. The 'n' notation in the suffix indicates that the absorption lines in the star's spectrum appear spread out and nebulous because of the Doppler effect from rapid rotation. The measured projected rotational velocity has been measured as high as 375 km s⁻¹. Meilland et al. (2007) estimate the pole of the star is inclined by 55° to the line of sight, yielding an equatorial azimuthal velocity of 470 km s⁻¹. This is close to the critical velocity where the star would start to breakup. The rapid rotation is causing a pronounced equatorial bulge of about 2.4–2.7 times the polar radius.