eclipsing binary

n.
A binary star whose components pass in front of each other, thereby causing a regular eclipse of one of the stars.

Double star systems in which the two components are too close to be seen separately but which reveal their duplicity by periodic changes in brightness as each star successively passes between the other and the Earth, that is, eclipses the other. Studies of the light changes and the radial velocity changes of each component permit the computation of the radii, masses, and densities of the components—important quantities that cannot be measured directly in single stars. In addition, these close double stars are useful in studies of mass loss and of stellar evolution. Since eclipsing stars are variable in light, they are included in general variable star catalogs under the same system of nomenclature. See also Binary star.

It is now believed that all explosive variables (novae, recurrent novae, and so forth), with the exception of supernovae, are members of close binary systems. At least some of the x-ray sources are close binaries in this state. In a few of the eruptive variables, particularly those known as dwarf novae, rapid scintillation is found, presumably in each system from a hot spot where the transferring mass collides violently with a circumstellar disk of relatively low-density material revolving around the collapsed star; the scintillation stops periodically when the spot is eclipsed by the other component. See also Nova; Stellar evolution.

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