Horace A. Smith
Michigan State University
ABSTRACT
At the dawn of investigations into RR Lyrae stars in globular clusters, observations by Solon Bailey demonstrated that RRab variables in different globular clusters occupied different loci in the period-amplitude diagram. It was much later before it was realized that the properties of cluster period-amplitude diagrams were correlated with Oosterhoff type and with globular cluster metallicity. Recent observations let us revisit the question of which parameters determine the location of the RRab period-amplitude diagram. We are closer to determining what are the rules governing the period-amplitude diagram, and what are the exceptions to those rules.