U Vulpeculae

 
U Vulpeculae is a variable and binary star in the constellation Vulpecula.
It is a classical Cepheid variable and its apparent magnitude ranges from 6.73 to 7.54 over a precise cycle of 7.99 days. Its variable nature was discovered in 1898 at Potsdam Observatory by Gustav Müller and Paul Kempf.
In 1991 a study of radial velocities showed that it U Vulpeculae is a spectroscopic binary and a full orbit with a period of 2510 days (6.9 years) was first calculated in 1996. The secondary star is invisible and is only known from its effect on the motion of the primary.