Variable Star Atlas - Semi-Regular Variables
Semi-Regular variables are cool, giant evolved stars on the asymptotic giant branch. These are stars at the ends of their lives and have expanded greatly since their birth. These variables have very long pulsation periods which range from 10 to >1000 days. SR types are stars that exhibit periodic variations with interruptions in their pulsation cycles that cause irregularities in their light curves, hence the name "Semi-Regular". A large fraction of semi-regular variables have two distinct modes of variability. These stars (called LSPs) have long secondary periods that are superimposed on shorter period variability.