3 Vulpeculae (abbreviated 3 Vul) is a binary star system in the northern constellation of Vulpecula, located around 366 light years away from the Sun. 3 Vulpeculae is its Flamsteed designation. It is visible to the naked eye as a faint, blue-white hued star with a baseline apparent visual magnitude of 5.18.
3 Vul has been nicknamed "the Observer's Nightmare" (or its Latin free translation, "Spectatori Error Inextricabilis") by some astronomers[1] [2] because it is difficult to study as its orbital period is close to a year, and additionally it is pulsating with a period close to a day.[2] From a twenty-year spectroscopic study, Hube and Aikman established a 367-day orbital period, and noted the presence of non-radial pulsations in the primary star. From sparse photometry, the authors also established the star's light variability. They suggested that the primary is a member of the 53 Persei class of variable stars.[3] Such stars are now collectively known by the term slowly pulsating B-type stars. Its photometric variation led to a variable star designation, as V377 Vulpeculae, but the non-reproducibility of the light curve made determination of the pulsation period elusive.
Continuous monitoring of the star by the Transiting Exoplanet Survey Satellite has revealed a beat-period phenomenon in the light curve, which causes the luminosity variations to fluctuate in amplitude. The pulsations are non-radial, that is, the star's photosphere varies in shape rather than volume; different parts of the star are expanding and contracting simultaneously. These gravity waves, or g-mode waves, can be indicative of the interior structure of the star.
The primary member, designated component A, is a most likely a B-type main-sequence star with a stellar classification of B6 III. The star has 4.16[2] times the mass of the Sun and is radiating 286 times the Sun's luminosity from its photosphere at an effective temperature of 14,343 K.[2] The secondary has an estimated 0.6–1.1 solar masses.[2]