SuperWASP Observations of Variable Stars

Eclipsing Binary Systems

A binary star is a stellar system that consists of two stars orbiting around their center of mass. It is estimated that about half of all stars are binary. If binaries orbit in a plane containing our line of sight, they will eclipse each other; these are called eclipsing binaries. When stars eclipse in this way it causes the brightness to vary, and this effects their light-curves because when a star is eclipsing another we see less light. The size of the stars, the distance between them and how much of the other star one star covers also determines how the curve may look.

Eclipsing binary systems are incredibly important at SuperWASP because the effects eclipsing binaries have on light-curves can be similar to that of some planets; as a planet will cause a dip in the brightness of a star when it orbits it like a star would do. Just knowing what kind of eclipsing binary system is present can be difficult enough, without the added challenge of distinguishing planets. Here are a few examples of eclipsing binary systems:

EA (Algol Type)

Algol (Beta Persei) type eclipsing systems have spherical or slightly ellipsoidal components. Using the light curves it is possible to specify the beginning and end of eclipses. Between eclipses the light remains almost constant. Secondary eclipses may not be visible if the stars are of considerably different sizes. Extremely wide ranges of periods have been observed, at roughly 0.2-10000 days. Light amplitudes are also quite varied and they can reach several magnitudes.

Here the stars are differently sized:

RV Crt

RU Lep

BN Peg

In this example the stars are of a similar size:

V796 Cyg

EB (Beta Lyrae Type)

Beta Lyrae-type eclipsing systems have ellipsoidal components. It is impossible to specify the beginning and end of eclipses because the brightness continuously varies in between eclipses. It is possible to see the secondary eclipse in every case, but it is generally smaller than that of the primary one. The periods are mainly longer than one day.

EP Aur

IP Lyr

RS (RS Canum Venaticorum Type)

RS Canum Venaticorum type variables are close binary systems. Their components have enhanced chromospheric activity that causes quasi-periodic light variability. They are x-ray sources and rotating variables.

V808 Tau

II Peg

UV For

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