Some types of stars change their brightness over time according to regular cycles, and these kinds of stars are called variable stars. RR Lyrae stars are a class of variable stars, and researchers have found that the material composing these stars can affect the rate at which they change their brightness. This article measures the composition of a sample of RR Lyrae stars and studies this phenomenon in more detail, helping astronomers better understand them.

http://www.raa-journal.org/raa/index.php/raa/article/view/1447