Delta Boötis

Delta Boötis, Latinized from δ Boötis, is a double star in the northern constellation of Boötes, forming the easternmost member of the constellation's kite-shaped asterism of brighter stars. Based upon parallax measurements, it is located at a distance of approximately 120.5 ly from the Earth. This star is sometimes called Princeps, meaning prince or prime in Latin. The origin of this name is unclear, although it usually appears in an astrological context. The apparent visual magnitude of this star is 3.5, making it visible to the naked eye even during a Full Moon. The magnitude 7.81 companion can be viewed in binoculars or a small telescope.

In Chinese, 七公 (Qī Gōng), meaning Seven Excellencies, refers to an asterism consisting of δ Boötis, 42 Herculis, τ Herculis, φ Herculis, χ Herculis, ν1 Boötis and μ1 Boötis. Consequently, the Chinese name for δ Boötis itself is 七公七 (Qī Gōng qī, the Seventh Star of Seven Excellencies.)

Properties
This system consists of a pair of stars located in physical proximity to each other and sharing a similar motion through space, suggesting that they may form a binary star system. Based upon their angular separation and their distance, they have a projected separation of 3,800 Astronomical Units (AU). If they are gravitationally bound to each other, the orbital period of the system would be at least 120,000 years.

The brighter member of the pair has a stellar classification of G8 III, indicating that it has exhausted the supply of hydrogen at its core and evolved into a giant star. It now has a radius more than eleven times the radius of the Sun. Compared to the Sun, this star appears deficient in elements other than hydrogen and helium—what astronomers term the star's metallicity. The outer envelope of this star has an effective temperature of 4,810 K, which is what gives it the characteristic yellow hue of a G-type star.

The secondary component has a stellar classification of G0 V, which suggests it is a main sequence star that may be similar in physical properties to the Sun. The apparent visual magnitude of this star is 7.81, making it much less luminous than the primary component.