Pulsations in red supergiants with high L/M ratio -- Implications for the stellar and circumstellar structure of supernova progenitors

TL;DR

This study explores how pulsations in red supergiants with high luminosity-to-mass ratios influence their pre-supernova structure and circumstellar environment, highlighting potential large amplitude pulsations and superwind phenomena.

Contribution

It provides new insights into the pulsational behavior of RSGs with high L/M ratios, linking stellar evolution, pulsations, and pre-supernova mass loss processes.

Findings

Pulsation period and growth rate increase with L/M ratio.

High L/M ratios can lead to large amplitude pulsations.

Pre-supernova changes may cause significant alterations in circumstellar medium.

Abstract

We investigate the pulsational properties of RSG models --- which we evolve from ZAMS masses in the range 10 to $20 \Msun$ --- 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 that 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 $10^4 \yr$ 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.