Boil-off of red supergiants: mass loss and type II-P supernovae

TL;DR

This paper presents a model for mass loss in red supergiants driven by shock waves and radiation pressure, explaining observed mass loss rates and their impact on supernovae characteristics.

Contribution

It introduces an analytic model of chromospheric mass loss in red supergiants, linking shock waves and radiation pressure to observed mass loss rates and supernova features.

Findings

Mass loss rates match recent observations.

Low-mass RSGs lose less mass; high-mass lose more.

Chromospheric mass influences early supernova light curves.

Abstract

The mass loss mechanism of red supergiant stars is not well understood, even though it has crucial consequences for their stellar evolution and the appearance of supernovae that occur upon core-collapse. We argue that outgoing shock waves launched near the photosphere can support a dense chromosphere between the star's surface and the dust formation radius at several stellar radii. We derive analytic expressions for the time-averaged density profile of the chromosphere, and we use these to estimate mass loss rates due to winds launched by radiation pressure at the dust formation radius. These mass loss rates are similar to recent observations, possibly explaining the upward kink in mass loss rates of luminous red supergiants. Our models predict that low-mass red supergiants lose less mass than commonly assumed, while high-mass red supergiants lose more. The chromospheric mass of our models is $\sim$0.01 solar masses, most of which lies within a few stellar radii. This can help explain the early light curves and spectra of type-II P supernovae without requiring extreme pre-supernova mass loss. We discuss implications for stellar evolution, type II-P supernovae, SN 2023ixf, and Betelgeuse.