What drives heavy mass loss in the final years before collapse?

Early spectra with narrow, short-lived emission lines (flash ionization) show dense circumstellar material within $\sim 10^{15}\,\mathrm{cm}$ in a large fraction of Type II supernovae, implying mass-loss rates $\sim 10^{-4}$ to $10^{-2}$ $M_{\mathrm{sun}}/\mathrm{yr}$ in the last years, far above steady red supergiant winds of $\sim 10^{-6}$ $M_{\mathrm{sun}}/\mathrm{yr}$. Identify the mechanism (wave energy transport from core convection in the last burning stages, binary interaction, pulsation-driven winds) and whether it also produces observed pre-explosion outbursts. Answer: a mechanism predicting circumstellar mass and extent versus progenitor mass and evolutionary stage.

Pre-explosion monitoring of many nearby supernova progenitors combined with early spectra, compared with predicted outburst timing and circumstellar masses.