A comparison of light and velocity variations in semiregular variables

NIR velocity variations are compared with simultaneous visual light curves for a sample of late-type semiregular variables (SRV). Precise radial veloc ity measurements are also presented for the SRV V450 Aql. Our aim is to inv estigate the nature of the irregular light changes found in these variables . Light and velocity variations are correlated in all stars of our sample. Ba sed on these results we discuss several possibilities to explain the observ ed behavior. We find that pulsation is responsible for large amplitude vari ations. In a recent paper Lebzelter (1999) invoked large convective cells t o understand observed velocity variations. This possibility is discussed wi th respect to the observed correlation between light and velocity changes. In the light of these results we investigate the origin of the semiregular variations.