It is shown that the binary technique - a B star companion is used as a light source which probes the wind of the red giant primary - has yielded accurate mass-loss rates and wind velocities for 8 G to M (super) giants and (in some cases) estimates of wind temperature.
Eclipsing binary systems have in addition revealed that G and K supergiants possess extended chromospheres which could be detected outwards to ∼ 1 R* stellar radius) above the photospheres. Electron temperatures Te and hydrogen ionization ne/nH seem to increase with height up to at least 0.5 R* (ne/nH= 10−2, Te = 104 K at 0.5 R*), and the winds start to be accelerated at heights above ∼ 0.5 R*.
Mass-loss rates appear to increase steeper than linearly with L/g · R. It is shown that the observed mass-loss rates are consistent with stellar evolution constraints for both Pop. II and Pop I stars.