It is estimated that out of all the stars in our universe, approximately half are locked in a binary system with another star. Of these, a significant portion are eclipsing binary stars. As the name implies, an eclipsing binary star system is a star system in which two stars lie in(or almost in) the same plane as each other, and as such, eclipse each other twice in one period. Although these may appear as a singular bright dot in the night sky, the two entities can be separated using tools such as spectroscopic and photometric measurements or even something as simple as a pair of binoculars. There are several different types of these stars, and they are as follows:
- E – The two stars eclipse frequently, and observers will see apparent changes in magnitude.
- EA – β Persei-type (Algol) eclipsing systems Binaries with spherical or slightly ellipsoidal orbits. Light amplitudes are different between stars.
- EB – β Lyrae-type eclipsing systems. Ellipsoidal orbits. §Impossible to see onset and end of eclipses.
- EP – Stars showing eclipses by their planets.
- EW – W Ursae Majoris-type eclipsing variables. Components almost in contact. Impossible to see onset and end of eclipses. Eclipses shorter than one day.
In order to analyze a pair of eclipsing binaries, one can utilize photometry and use data acquired through that to build a light curve for the pair, which displays the magnitude(brightness) of the system over time, with noticeable dips in the magnitude representing eclipses. The curve for the star system GG Lup is shown below.
The aforementioned dips in magnitude are very visible in this light curve, and the bigger drop indicates that the cooler star is eclipsing the hotter, brighter star – an equivalent amount of surface area is being enveloped during each eclipse. In addition, the spike-like nature of the drops indicate that this system experiences partial eclipses – a flat bottom is the mark of a total eclipse. Using star classifications, approximate temperature ratios could be calculated for the system as a whole, and using spectral measurements, Doppler shift could be found as well to determine the movement of the star system toward or away from us. Ultimately, however, many advancements in astronomical research tools will be needed in order to calculate absolutes for each star, such as radius.
Here’s a cool simulation you can use to model your own binary star system(be sure to enable Flash)! https://astro.unl.edu/naap/ebs/animations/ebs.html