Magnitude 5.7 Apparent magnitude (V) 5.7 | ||
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Theta Apodis (θ Aps, θ Apodis) is the Bayer designation for a star in the southern circumpolar constellation of Apus. It is a variable star with a mean apparent visual magnitude of 5.7, 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 370 light-years (110 parsecs), based upon parallax measurements made from the Hipparcos spacecraft. 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 3151 K. It is a semiregular pulsating variable and its brightness changes over a range of 0.56 magnitudes with a period of 119 days. 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 (0.041 pc) 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.