Many Wolf Rayet stars are found in close binary systems that consist of a massive, luminous, main-sequence 0 star and a less massive, smaller, yet even more luminous companion. Because it is so luminous, the small star expels the outer parts of its atmosphere in the form of a dense stellar wind, winch produces a […]

It is reasonable to assume that the two stars in a binary system formed at the same time. The chance of a collision between two single stars in the Galaxy is very small; t he chance of the capture of one by another of a different age to form a binary system smaller still. It […]

Of course, not all eclipsing binaries can be analysed in the way we have described above; often a certain amount of guess-work has to be employed. A case of particular interest is the star £ Aurigae. This is an eclipsing binary system consisting of a small, blue, bright B star with radius 5 solar radii […]

When mass transfer is taking place from one star to the other in a binary system, there is a considerable amount of gas flowing in the Roche lobe of the star that is receiving the mass. The splash as the gas stream strikes the star is probably sufficient to produce a flow of gas around […]

As a star evolves and burns its nuclear fuel its radius slowly in-creases If, therefore, the star is in a binary system it is possible for it, during the course of evolution, to swell up and inter¬act with and possibly even to engulf a companion star. If the two stars are near enough together for […]

We have seen that the light curve of an eclipsing (or of a nearly eclipsing) binary system can be complex and difficult to interpret. The most important effects that must be taken into account are the following DISTORTION :A single star, like the Sun, is essentially spherical. When two stars are close together, however, mutual […]

This group of stars, of which the prototype is W Ursae Majoris, are binary stars that are so close together that they are in contact. The binary system consists of two stellar cores, orbiting around one another, surrounded by a common envelope. Again, the light curve varies smoothly around the cycle often varying from cycle […]

When ellipsoidal variables eclipse, they produce a light curve that is typified by the star system 0 Lyrae. Because the stars are distorted, the light curve away from an eclipse is not flat, but rather shows a smooth variation. Moreover, in general, the surface of a star is not uniformly bright, because of limb darkening, […]

We noted above that when the two binary stars are spherical, the light curve remains constant outside of eclipses. However, when two stars are close enough together, the force of gravity is so high that each component raises huge tides on the other, so that both are pulled out to form elongated egg shapes. When […]

The simplest case to consider is that of two stars that are both spherical that both appear uniformly bright over their surface (no limb darkening), and that have circular orbits. In this case we can easily distinguish between the two different types of eclipse, partial and total. When i is close enough to 90° for […]