1.5 How do Stars Lose their Mass?

Strafella et al. (1998) discuss the physical processes through which stellar mass ejection can occur. They are; (i) radiative pressure, arising from the transfer of momentum from photons to the stellar atmosphere. (ii) Centrifugal force, see Section 1.10.1. (iii) Thermal expansion of a high-temperature gas; a convection zone beneath the photosphere can generate waves that propagate upward and dissipate in the outer stellar atmosphere. (iv) Hydromagnetic waves, also in the convection zone beneath the photosphere. These waves take the form of an Alfvén wave. The ionized plasma is frozen to the magnetic field and partakes in the wave motion which releases its kinetic energy into the gas surrounding the star.