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 […]
When the orbital inclination i is sufficiently clone do 90″, we can nee the two components of a binary system eclipse each other. The graph of the apparent magnitude of the binary system against time is known as the LIGHT CURVE. In general the light curve of an eclipsing binary star displays two dips, or […]
Many stars t hat appear as a single pinpoint of light in the sky, when examined by means of a spectroscope produce a spectrum which appears to be the combination of the spectra from two separate stars. If the relative positions of features on the two spectra remain unaltered, the stars are known as a […]
If a binary system is close enough to us, we can see each component as a separate point of light, each of which moves round the other in a regular manner. At each point in time we can plot the positions of each star in the sky. In time each star traces out a spiral […]
When we have made observations of a binary system of stars, we wish to be able to deduce a set of numbers that describe completely the orbit of the stars in time and space. This set of parameters is known as the ORBITAL ELEMENTS of the binary system. As we shall see, it is not […]