Theta Apodis

Theta Apodis (θ Apodis, θ Aps) is a variable star in the southern circumpolar constellation of Apus. It is a variable star with an apparent visual magnitude range of 4.65 to 6.20, which, according to the Bortle Dark-Sky Scale, means it is a faint star but visible to the naked eye from dark suburban skies. The distance to Theta Apodis is approximately 350 ly, based upon parallax measurements made from the Gaia telescope. It is unusual in that it is a red star with a high proper motion (greater than 50 milliarcseconds a year).

This is an evolved red giant that is currently on the asymptotic giant branch, with a stellar classification of M7 III. It shines with a luminosity approximately 3879 times that of the Sun and has a surface temperature of $3,131 K$. It is a semiregular pulsating variable and its brightness changes over a range of 0.56 magnitudes with a period of 119 days. A longer period of around 1,000 days has also been detected. It is losing mass at the rate of 1.1 × 10−7 times the mass of the Sun per year through its stellar wind. Dusty material ejected from this star is interacting with the surrounding interstellar medium, forming a bow shock as the star moves through the galaxy. The stand-off distance for this front is located at about 0.134 ly from Theta Apodis.

Theta Apodis has been identified as an astrometric binary, indicating that it has an orbiting companion that causes gravitational perturbation of the primary star.