Variability in the H-R Diagram: Early F Stars and Late-Type Giants

Dr. Francis C. Fekel

Center of Excellence in Information Systems

Tennessee State University, Nashville TN

As a byproduct of several photometric and spectroscopic survey programs the light and velocity variability of several types of variables stars has recently been examined. Gamma Doradus stars are a newly identified group of variables on the cool side of the instability strip. A survey is in progress to further define this class. Spectroscopic observations that a significant fraction have cool disks. A recent survey of G and K giants found 43% had light variability, most likely as a result of radial and non-radial pulsation. Some semiregular variables have light variations with periods significantly longer than the corresponding fundamental modes. A group of these stars was investigated spectroscopically and the variability has been examined to determine the mechanism of variability, duplicity or pulsation.