Winds from Cool Red Giants and Hot, Massive Stars
- For cool Red Giant stars, P-Cygni profiles suggest relatively slow speeds, 10-50 km/s, but with mass loss rates up to million times that of the solar wind, i.e., ~ 10-8 MO/yr.
- For these cool-star winds, the driving mechanism is not well understood, but may involve a combination of stellar pulsation, Alfvèn wave pressure, or radiation pressure on dust.
- But massive, hot stars show the strongest winds, with speeds sometimes exceeding 3000 km/s, and mass loss rates up to a billion times the solar wind, i.e. ~ 10-5 MO/yr !
- This is large enough that, during the course of their relatively brief (~107 yr) evolutionary lifetime, such massive stars can be stripped of their entire hydrogen envelope, exposing a “Wolf-Rayet” star characterized by strong line emission from ions of n