Delta Aquilae

Delta Aquilae (δ Aquilae, δ Aql) is a binary star system in the equatorial constellation of Aquila. It has an apparent visual magnitude of 3.4 and, based upon parallax measurements, is located about 50.6 light-years (15.5 parsecs) from Earth.

Delta Aquilae is an astrometric binary where the two components orbit each other with a period of 3.422 years and an eccentricity of about 0.36. This is a type of binary star system where the presence of the secondary component is revealed by its gravitational perturbation of the primary. The individual components have not been resolved with a telescope.

The primary component, Delta Aquilae A, is a subgiant star with a stellar classification of F0 IV, where the luminosity class of IV indicates it is in the process of exhausting the supply of hydrogen at its core and evolving into a giant star. The mass of the star is 65% greater than the Sun and it has expanded to more than double the Sun's radius. It is radiating around 7–8 times the luminosity of the Sun from its outer atmosphere at an effective temperature of 7,016 K, giving it the yellow-white hue of an F-type star. Delta Aquilae A is a Delta Scuti variable that exhibits variations in luminosity caused by pulsations in its outer envelope. It is spinning rapidly with a projected rotational velocity of about 87 km s−1. This is a lower bound on the azimuthal velocity along the star's equator.

The secondary component, Delta Aquilae B, is a smaller star with about 67% of the Sun's mass and an estimated 61% of the radius of the Sun. It may be a K-type star.