Eclipsing Binaries

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A binary star is a star system consisting of two stars orbiting around a common center of mass(barycenter). The brighter star is the primary and the other is its companion star and is called the secondary. With eclipsing binaries the orbital plane of the two stars lies along the line of sight of the observer so that the components eclipse each other at different points in their orbit. Algol is the best-known example of an eclipsing binary.

When the binary system is also a spectroscopic binary and the parallax of the system is known, the binary can be used for stellar analysis. The measurement of the parameters of these systems has become possible with 8 meter telescopes. This capability makes them usable as standard candles. During recent studies they have been used to give direct distance estimates to the Large Magellanic Cloud, the Small Magellanic Cloud, the Andromeda Galaxy, and the Triangulum Galaxy. They can be used as a direct method to gauge the distance to galaxies to within a 5% accuracy.

These systems are variable stars. The variability has nothing to do with the components of the stars, but because of the eclipses. If one of the stars is larger than the other, one will be obscured by a total eclipse while the other will be obscured by annular eclipse. The orbital period of an eclipsing binary can be determined by studying the light curve. The relative sizes of each star can be determined in terms of the radius of the orbit by observing how quickly the brightness changes as the disc of the near star slides over the disc of the distant star. If the system is also a spectroscopic binary, the orbital elements can also be determined. This allows for the determination of the masses and densities of each component.

Binary systems are much more common than thought in the past. As the occurrence of binaries increases, does does the instance of eclipsing binaries. As such, the interest of astronomers is becoming more intense. That all means that there is more science to come.

We have written many articles about eclipsing binaries for Universe Today. Here’s an article about binary stars, and here’s an article about Algol.

If you’d like more info on the eclipsing binaries, check out these articles from NASA and Hyperphysics.

We’ve also recorded an entire episode of Astronomy Cast all about Binary Stars. Listen here, Episode 152: Binary Stars.

References:
http://en.wikipedia.org/wiki/Binary_star
http://csep10.phys.utk.edu/astr162/lect/binaries/algol.html

Tagged as: binary stars, eclipsing binaries