Gamma Arae

The proper motion of this star traces back to the Scorpius region of the Galactic Plane, about 20–25° away. Gamma Arae has an optical companion located at an angular separation of 17.9 arcseconds, which is an A-type main sequence star with an apparent magnitude of 10.5.

Properties

This is an enormous star with 14 times the radius of the Sun. It is radiating 120,000 as much energy as the Sun from its outer envelope at an effective temperature of 21,240 K. This heat gives the star the blue-white glow of a B-type star. The spectrum shows it to match a stellar classification of B1 Ib, with the luminosity class of 'Ib' indicating this is a lower luminosity supergiant star. It is a relatively young body, with an estimated age of around 15.7 million years.

Gamma Arae is rotating rapidly with a projected rotational velocity of 269 km s⁻¹, causing it to complete a full rotation about every 4.8 days. In the spectrum of this star, this high rate of spin is causing absorption lines to blend together because of the Doppler effect, making them more difficult to analyze. It is a periodically variable star that undergoes non-radial pulsations with a primary period of 1.1811 days and a secondary period of 0.1281 days.

There is some disagreement about the mass of this star in the literature. Tetzlaff et al. (2011) estimate the mass as 12.5±0.6 solar masses, while Fraser et al. (2010) give a mass of around 19 and Lefever et al. (2007) lists a value of 25. It is shedding mass through its stellar wind at the rate of 3.0×10⁻⁸ solar masses per year, which is equivalent to losing the mass of the Sun every 33 million years. The wind is being affected by the star's rapid rotation, resulting in an enhanced outflow along the equator.