- Algol variable
Algol variables or Algol type binaries are a class of eclipsing
binary star s. When the cooler component passes in front of the hotter one, part of the latter's light is blocked, and the totalbrightness of the binary, as viewed fromEarth , temporarily decreases. This is the primary minimum of the binary. Total brightness may also decrease, but less, when the hotter component passes in front of the cooler one; this is the secondary minimum.The period, or time span between two primary minima, is very regular, being determined by the revolution period of the binary, the time it takes for the two components to once orbit around each other. Most Algol variables are quite close binaries, and therefore their periods are short, typically a few days. The shortest known period is 0.145 days (~3.48 hours, VZ Sculptoris); the longest is 9892 days (27 years,
epsilon Aurigae ).Component stars of Algol binary systems have a spherical, or slightly ellipsoidal shape. This distinguishes them from the so-called
beta Lyrae variable s andW Ursae Majoris variable s, where the two components are so close thatgravitation al effects lead to serious deformations of both stars.Generally the
amplitude s of the brightness variations are of the order of one magnitude, the largest variation known being 3.4 magnitudes (V342 Aquilae). The components may have any spectrum, though in most cases the brighter component is found to have B, A, F, or G spectra.The prototype of the Algol type
variable star s isAlgol , or beta Persei. Its variability was first recorded in 1667 byGeminiano Montanari . The mechanism for its being variable was first correctly explained byJohn Goodricke in 1782.Many thousands of Algol binaries are now known: the latest edition of the [http://www.sai.msu.su/gcvs/gcvs General Catalogue of Variable Stars] (2003) lists 3,554 of them (9% of all variable stars). Data for some interesting Algol variables are given in the
list of known variable stars .References
[http://www.physics.sfasu.edu/astro/ebstar/ebstar.html Eclipsing Binary Stars] , D. Bruton (Stephen F. Austin State University)
Wikimedia Foundation. 2010.