U Aquilae is a

binary star A binary star or binary star system is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved as separate stars us ...

system in the constellation Aquila, Located approximately away from Earth. The primary star (component A) is a

yellow supergiant A yellow supergiant (YSG) is a star, generally of spectral type F or G, having a supergiant luminosity class (e.g. Ia or Ib). They are stars that have evolved away from the main sequence, expanding and becoming more luminous. Yellow supergiants ...

with a radius of and a luminosity of . The secondary (component B) is a blue main-sequence star, twice the mass of the sun and around thirty times more luminous. It is hotter than the primary star at 9,300 K, but much smaller and fainter. The two stars orbit every five years and their separation varies from five to seven

astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

s in a mildly eccentric orbit. Discovery of the variability of U Aquilae was announced by Edwin F. Sawyer in 1886. In his announcement, he called the star 50 Aquilae, which is its designation in ''Uranometria Argentina''. Sawyer had begun observing the star in late 1882, and had derived a period of "about one week". It was listed with its

variable star designation In astronomy, a variable-star designation is a unique identifier given to variable stars. It extends the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in whic ...

, U Aquilae, in

Annie Jump Cannon Annie Jump Cannon (; December 11, 1863 – April 13, 1941) was an American astronomer whose cataloging work was instrumental in the development of contemporary stellar classification. With Edward C. Pickering, she is credited with the creation of ...

's 1907 ''Second Catalogue of Variable Stars''. U Aquilae A is a

classical Cepheid Classical Cepheids are a type of Cepheid variable star. They are young, population I variable stars that exhibit regular radial pulsations with periods of a few days to a few weeks and visual amplitudes ranging from a few tenths of a magnitude u ...

variable star, ranging between magnitudes 6.08 and 6.86 over a period of 7.02 days. It is an evolved star which has exhausted its core hydrogen and is now fusing helium into carbon.

References

{{DEFAULTSORT:U Aquilae Aquila (constellation) Binary stars Classical Cepheid variables Aquilae, U 183344 7402 095820 Durchmusterung objects F-type supergiants B-type main-sequence stars F-type bright giants