Southern Eclipsing Binaries Project

Overview of Eclipsing Binaries

Historically EB research has been vital as a step in establishing the distance scale of the universe, providing distance measures with ~5% accuracy as far as the Magellanic Clouds and nearby galaxies such as M31. This is because combined photometric and spectroscopic measures can directly establish absolute parameters of the stars, such as mass, radius, luminosity and distance. For individual stars such data can usually be inferred only indirectly. The General Catalogue of Variable Stars (Samus, N.N. et al, 2007-2015, VizieR online data catalogue B/GCVS), whose entries should be read with a raised eyebrow, classifies eclipsing binaries morphologically by light curve shape into three groups EA (Algol-like light curve), EB (beta Lyrae-like) and EW (W UMa-like). Read the definitions here. Below are the phased light curves of the prototypes, L to R Algol (Beta Per), Beta Lyr and W UMa. Those three light curve classifications relate approximately to the physical/geometric classification known as Roche Geometry, which considers whether the photospheres of the two stars are in contact with the L1 Lagrange point of neutral gravitational attraction between the two stars (at the crossover of the figure-8 “Critical Roche Surface” in these two-dimensional diagrams.) Think of the figure 8 as a mountain contour defining two craters with the stars at the bottom. Fill one with water to the crossover L1 point, and its water will spill through L1 into the other. Overfill both and a single two-lobed lake is formed. Clockwise from top left: Detached  binary, typically has EA-type light curve. Near-contact, stars gravitationally distorted, typically EB- type. Semi-detached system, many different light curve types, Algol is like this (!) as are cataclysmic binaries. Left star spills its atmosphere through the L1 point onto the other star. Over-contact system, stars have a common photosphere whose circulation ensures surface temperatures of both “stars” and hence eclipse depths are similar; typically EW-type light curve.

Further Reading

Aside from surfing the WWW (AAVSO is authoritative, Wikipedia often good on specialized articles, CALEB is vital, and look for academic websites), here are important books: Foster, G. Analyzing Light Curves, a Practical Guide. Self-published through Hilditch, RW. An Introduction to Close Binary Stars, Cambridge 2001. Percy, JR. Understanding Variable Stars, Cambridge 2007. (General) Sterken, C & C. Jaschek (eds), Light Curves of Variable Stars, a Pictorial Atlas. Cambridge 1996. (General) Terrell, D., J.D Mukherjee, R.E Wilson. Binary Stars, a Pictorial Atlas. Malabar Fla., Kreiger, 1992.
Page author: TJR Last edit: 2016-03-19