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 evolve 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 fundamental 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 values are obtained at and beyond central He-exhaustion due to major internal rearrangements of the nuclear burning regions. Our non-linear calculations as well as the behavior of the linear period and growth rate of the pulsations for periods approaching the Kelvin-Helmholtz time scale of the H-rich stellar envelope point towards the possibility of large amplitude pulsations. Such properties are similar to those found in AGB stars and suggest the possibility of a "superwind" to occur before the RSGs explode as supernovae. We conclude that changes in global stellar properties during the last few 10⁴ yr before core collapse may lead to drastic changes in the pulsational and wind properties of pre-supernova stars, with marked consequences for the immediate pre-supernova structure of the star and the circumstellar medium. We compare our results with observations of long-period OH/IR variables and discuss observational evidence for our scenario from observed supernova light curves, spectra and remnants.