2026ApJ...996...18S

We investigate the evolution of red supergiant (RSG) progenitors of core-collapse supernovae (SNe) with initial masses between 12 and 20 M_⊙, focusing on the effects of enhanced mass loss due to pulsation-driven instabilities in their envelopes and subsequent dynamical ejections during advanced stages of nuclear burning. Using time-dependent mass loss from detailed Modules for Experiments in Stellar Astrophysics (MESA) stellar evolution models, including a parameterized prescription for pulsation-driven superwinds and time-averaged mass-loss rates attributed to resulting shock-induced ejections, we construct the circumstellar medium (CSM) before the SN explosion. We calculate resulting CSM density profiles and column densities considering the acceleration of the stellar wind. Our models produce episodes of enhanced mass loss (∼10^–4-10^–2M_⊙ yr^–1) in the last centuries-decades before explosion forming dense CSM (≳10^–15 g cm^–3 at distances ≲10¹⁵ cm)-consistent with those inferred from multiwavelength observations of Type II SNe such as SN 2023ixf, SN 2020ywx, SN 2017hcc, SN 2005ip, and SN 1998S. The formation of such dense circumstellar shells, within the explored range of our single star RSG models, provides a natural explanation for observed flash-ionization signatures, X-ray and radio emission, and has important implications for dust formation around Type II SNe.