Most 'Variable Stars' are not Varying at all..

They are ordinary stars that have a large orbiting planet.
Their light moves at c+vsin(t/T) towards Earth, causing the photon stream to
spatially bunch up and separate as it travels. This gives the impression of a
periodic brightness variation when it reaches an Earth observer.

For a complete discription of the process see:

http://www.scisite.info/The_new_ball..._of_light.html