Introduction
Stellar mass loss has been systematically derived from observations and is present in almost all regions of the HR diagram. The blueshifted circunstellar absorption lines, present in the spectra of late-type giant and supergiant stars, are interpreted as indicating the presence of cool and massive winds (Reimers, 1975; Goldberg, 1979; Castor, 1981; Hartmann, 1981; Cassinelli and MacGregor, 1982), with terminal velocities inferred (u?) to be lower than the surface escape velocity (veo) (Deutsch, 1956, 1960; Weymann, 1962). Several acceleration mechanisms have been proposed for driving these winds and one of the most promising involves the mass loss by an outward-directed flux of Alfvén waves (Belcher and Olbert, 1975; Haisch, Linsky and Basri, 1980; Hartmann and MacGregor, 1980; Jatenco-Pereira and Opher, 1989). For late-type giant and supergiant stars, this nonthermal energy flux must be deposited in the region of subsonic flow to explain the observed u? < veo (Leer and Holzer, 1980).
From observations we have: (1) a mean temperature T ? 104 K; (2) terminal velocities inferred: u? ? 50 km s -1, lower than the surface escape velocity veo, and (3) the mass loss rate dM/dt ? 10 -6 - 10 -7 M? ano -1.
We have direct evidence for Alfvén waves in the solar wind. Waves are observed with large perturbations in the magnetic field, with negligible density perturbations, indicating the presence of Alfvén waves. On the other hand, the theory that the solar corona is heated by hydro-magnetic waves is interesting by naturally adjusting on the solar corona structure and also implies probable momentum source to the solar wind (Stein & Leibacher, 1981).