PULSATIONS IN RED SUPERGIANTS WITH HIGH L M RATIO - IMPLICATIONS FOR THE STELLAR AND CIRCUMSTELLAR STRUCTURE OF SUPERNOVA PROGENITORS/

We investigate the pulsational properties of RSG models-which we evolv e from ZAMS masses in the range 10 to 20 M.-by means of linear and non -linear calculations. We find period and growth rate of the dominant f undamental mode to increase with increasing luminosity-to-mass ratio L /M. Our models obtain relatively large L/M values due to the inclusion of rotation in the evolutionary calculations; however, the largest va lues are obtained at and beyond central He-exhaustion due to major int ernal rearrangements of the nuclear burning regions. Our non-linear ca lculations as well as the behavior of the linear period and growth rat e of the pulsations for periods approaching the Kelvin-Helmholtz time scale of the II-rich stellar envelope point towards the possibility of large amplitude pulsations. Such properties are similar to those foun d in AGE stars and suggest the possibility of a ''superwind'' to occur before the RSGs explode as supernovae. We conclude that changes in gl obal stellar properties during the last few 10(4) yr before core colla pse may lead to drastic changes in the pulsational and wind properties of pre-supernova stars, with marked consequences for the immediate pr e-supernova structure of the star and the circumstellar medium. We com pare our results with observations of long-period OH/IR variables and discuss observational evidence for our scenario from observed supernov a light curves, spectra and remnants.