Improving our understanding of SRC variable stars

Abstract

SRC variables are evolved stars (mostly M supergiants) that vary in brightness with semi-regular periods ranging from several months to several years. Their light variation is caused by a combination of pulsation, convection, and other processes such as dust ejections. Much data exist for the stars, but they have been under-utilized. We studied 49 individual SRC variables using archival and newly-obtained data. We present new results including cyclic variation in radial velocity, spectral type, and luminosity class, period analysis, and changes in period and mean magnitude for individual stars. We have re-examined the period-luminosity and period-radius relations, and discovered a new relationship among spectral type, luminosity class, and light amplitude. To aid in future studies of the stars, we have subdivided them into three categories based on the quality of available data and the likelihood that they are periodic rather than simply varying irregularly.