Eclipsing binaries¶
Many stars are in binary systems (or even higher multiples) and some are oriented such that, at regular points in their orbits, one star passes across our line of sight to the other, obscuring its light in an eclipse. (When a planet obscures its host star, the same phenomenon is a transit.) These systems are the eclipsing binaries. Their light curves are traditionally distinguished into three classes, which I’ve indicated under sections that try to reflect the relevant physical properties of the system, which depend on how far apart the two stars are.
Two extreme cases are easier to understand. In wide binaries, the stars are not dramatically distorted by the gravity of their companions. Between the eclipses, we see the total light of two separate stars and it is clear when the eclipses begin and end. In close binaries, the two stars are so close together that their surfaces basically touch. The system’s apparent brightness varies continuously and it is impossible to tell when the eclipses begin and end or distinguish which eclipse is caused by which star.
Finally, there are the intermediate binaries. Here, the stars are close enough that they are significantly distorted by their companion’s gravity but one can still identify two distinct eclipse depths.