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A star is generally termed "variable" when its brightness or color
variations are on time scales of the order of about 100 years or less. The
form of these variations may be periodic, semi-periodic, or irregular.
There are elaborate taxonomies of variable stars, the main types being
eruptive variables, pulsating variables, rotating variables, cataclysmic
variables, and eclipsing binary systems. Astronomers study variable stars
to learn about stellar structure and evolution and because certain types of
variable stars are key to the determination of astronomical distances.
In recent years, automated surveys of the sky have harvested very large
numbers of variable stars, often as a by-product of the main purposes of
the survey. These large databases are just now being exploited and are
likely to have a major impact on understanding of variable stars.
In this talk I will give an overview of variable stars and of some of the
statistical problems that arise. In particular I will discuss the problem
of estimating the period of an unknown smooth function sampled at irregular
times.
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