The Stellar-Wind Regions.

From the observations of the solar wind and of the M giant a Herculis the gross dynamical features of the stellar-wind regions associated with class G main-sequence and M giant stars are given for various interstellar environments. The supersonic wind from a class G star undergoes a shock transition to subsonic flow at a radial distance of 1O-1O a u. This subsonic flow will be subject to turbulence and other instabilities in many cases. The wind from an M giant may extend many parsecs if the M-giant phase of evolution lasts as long as 1O years; the resultant interstellar contamination and heating are important. A rough calculation of the cavity formed by a stellar wind in a large-scale interstellar magnetic field shows that the cavity shape and dimensions for stationary flow depend on the pressure at infinity. As the pressure increases, the cavity changes from a circular cylinder of infinite radius, through an increasingly bulbous shape of finite radius, to a sphere of infinite radius with one finite cylindrical channel from each pole.