Theta Andromedae

Theta Andromedae is a binary star system in the northern constellation of Andromeda. Theta Andromedae, Latinized from θ Andromedae, is its Bayer designation. It is located at a distance of approximately 173 ly from the Sun, and has an apparent visual magnitude of 4.6. On the Bortle Dark-Sky Scale, this makes it visible to the naked eye from outside urban regions. Based on its motion through space, this system appears to be a member of the Sirius supercluster.

The brighter component is a white hued A-type main-sequence star with a stellar classification of A2 V. It is one of the least photometrically variable stars known. The star shows a high rate of rotation with a projected rotational velocity of 102 km/s. It has an estimated 2.8 times the mass of the Sun and is radiating 113 times the Sun's luminosity from its photosphere at an effective temperature of 8,960 K. The relatively high chemical abundances of iron and heavier elements suggests it may be a fast rotating Am star.

A stellar companion was detected in 1986 and reported in 1989. This fainter companion is separated from Theta Andromedae by 0.06 arcseconds. The secondary appears to be a massive, possibly A-type, star orbiting at a distance of around one astronomical unit with a period of 1033 days and a large orbital eccentricity (ovalness) of 0.95.

Naming
In Chinese, 天廄 (Tiān Jiù), meaning Celestial Stable, refers to an asterism consisting of θ Andromedae, ρ Andromedae and σ Andromedae. Consequently, the Chinese name for θ Andromedae itself is known as 天廄一 (Tiān Jiù yī, the First Star of Celestial Stable.)