Eclipsing Variables

The distinctive light curve of an eclipsing variable is easy to identify. Typically, the light remains steady for most of the time, with two evenly spaced drops in brightness. Depending on the relative sizes and brightness of the eclipsing stars, one minimum may be shallower than the other, or they may be equal.

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cataclysmic variables

Spectacular but generally unpredictable, cataclysmic variables are usually seen in close binary systems where the more massive star has evolved to a white dwarf and the less massive star is in its giant phase. In such cases, the white dwarf's gravity may be enough to pull material away from its companion onto itself. The dwarf star builds up a hot, dense atmosphere that can eventually detonate in a burst of nuclear fusion. The result is a nova, and the cycle can repeat many times, at predictable or

British astronomer John Goodricke (17641786) overcame profound deafness to become a gifted mathematician and observer. He invented the "light curve," and demonstrated that the star Algol, or Beta (b) Persei, varied with a regular period. He died at age 22 from pneumonia contracted while observing.

unpredictable intervals. Even more spectacular are Type Ia supernovae. These occur when a particularly massive white dwarf in a nova system gains enough mass to tip it over the Chandrasekhar limit (see p.37), causing it to collapse into a neutron star.

rotating variables

A recently recognized type of variable is a rotating star in which some areas of the surface are brighter than others— perhaps due to dark starspots (like our Sun's sunspots) or a bright "hot spot" like the one on Betelgeuse. As the star's rotation carries the darker or brighter region in and out of view, its brightness can vary. Another type occurs when stars are stretched into an ellipse by rapid rotation or the gravity of a binary companion. These vary in brightness as we see different amounts of the surface.

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