Does a red giant star produce more stellar wind than a yellow star?

Question

Do red giant stars produce more stellar wind than when they were ordinary yellow stars? If so, how big a difference are we talking about?

Answer 1

The Sun's current mass loss rate - a combination of the solar wind and radiation from the Sun - amounts to something like $10^{-13}$ solar masses per year.

The mass loss rates from red giant stars are variable, but much larger, and dominated by wind losses, rather than radiation. A common parameterisation of the average mass loss rate is the Reimers mass-loss rate (or variants thereof, e.g. Schroeder & Cuntz 2005) $$ \dot{M} = -\eta \frac{L R}{M}\ (M_\odot /{\rm year})$$ where $L$, $R$ and $M$ are the luminosity, radius and mass of the red giant in solar units and $\eta$ is a fitting parameter that must be determined empirically and is about $4\times 10^{-13}$ in this unit system.

For a typical red giant with $M=2M_\odot$, $L=1000 L_\odot$ and $R=100R_\odot$, the Reimers formula gives $2\times 10^{-8}$ solar masses per year. However, for the very biggest giants and during pulsational mass loss during the AGB phase, mass loss rates could reach $10^{-6}$ solar masses per year or more.

An aside

Since a star spends a few per cent of its life as a big red giant, but has 5-6 orders of magnitude bigger mass-loss rate during this time, you can easily see that most mass loss occurs when the star is a red giant.