Radiative time scales

Optically thin: radiative time scales are scale independent.
M dwarf:
- time_radiative=400 sec
- time_hydro=0.1 sec
- It takes some time to reach radiative equilibrium.
M supergiant:
- time_radiative=400 sec
- time_hydro=20000 sec
- Radiative-energy-exchange terms are stiff.
- Simulations of red supergiants are extremely CPU-time consuming compared to local solar models.
- Convection is in a different regime.

Left: very early CO5BOLD toy models of "Betelgeuse",
top: APOD 2000-12-22,
bottom: grid: 51³; CS11 (1999).