VV Cephei

The fact that VV Cephei is an eclipsing binary system was discovered by American astronomer Dean McLaughlin in 1936. VV Cephei experiences both primary and secondary eclipses during a 20.3 year orbit. The primary eclipses totally obscure the hot secondary star and last for nearly 18 months. Secondary eclipses are so shallow that they have not been detected photometrically since the secondary obscures such a small proportion of the large cool primary star. while the dominant period for longer wavelengths is 118.5 days. The short wavelength variations are thought to be caused by the disc around the hot secondary, while pulsation of the red supergiant primary caused the other variations. It has been predicted that the disc surrounding the secondary would produce such brightness variability. ==Spectrum==

The spectrum of VV Cep can be resolved into two main components, originating from a cool supergiant and a hot small star surrounded by a disk. The material surrounding the hot secondary produces emission lines, including [FeII] forbidden lines, the B(e) star|B[e] phenomenon known from other stars surrounded by circumstellar disks. The hydrogen emission lines are double-peaked, caused by a narrow central absorption component. This is caused by seeing the disk almost edge on where it intercepts continuum radiation from the star. This is characteristic of shell stars. The spectrum varies dramatically during the primary eclipses, particularly at the ultraviolet wavelengths produced most strongly by the hot companion and its disc. The typical B spectrum with some emission is replaced by a spectrum dominated by thousands of emission lines as portions of the disc are seen with the continuum from the star blocked. During ingress and egress, the emission line profiles change as one side or the other of the disc close to the star becomes visible while the other is still eclipsed. ==Distance==

The distance to VV Cephei is uncertain. The star is often considered a member of the Cepheus OB2 association, which contains another large supergiant star, Mu Cephei. The Hipparcos and Gaia Data Release 2 parallax measurements imply distances of 0.752 and 0.6 kiloparsecs respectively, while an analysis by Bailer-Jones et al. using the Gaia Data Release 3 parallax provide a photogeometric distance of 1.02 kpc. Assuming the Gaia DR3 distance, its KS band absolute magnitude would be gauged at −10.2. A 2004 study gives a higher distance of  kpc based on comparisons of linear and angular orbits, ==Properties==

Mass It should be possible to calculate the masses of eclipsing binary stars with some accuracy, but in this case mass loss, changes in the orbital parameters, a disk obscuring the hot secondary, and doubt about the distance of the system have led to wildly varying estimates. The traditional model, from the spectroscopically derived orbit, has the masses of both stars around , which is typical for a luminous red supergiant and an early B main sequence star. Radius Radius estimates of VV Cephei vary widely. Early estimates of the radius of the primary range from 1,200 to 1,600 solar radii, with an upper limit of . The Roche lobe is calculated to be about , thus the radius cannot be larger than this. ==See also==