Resumen
We discuss the expansion of an initially self-gravitating, static, singular cloud core characterized by a power-law density distribution, rho ~ r^-n, with 3/2 < n < 3. This core is heated out of mechanical balance by the formation of a massive star at its center. If the initial ionization and heating is approximated to occur instantaneously at t = 0, the subsequent flow (for r >> 100 AU) caused by the resulting imbalance between self-gravity and thermal pressure is self-similar. Because of the steep density profile, pressure gradients produce a shock front that travels into the cloud, accelerating the gas to supersonic velocities in what has been called the ``champagne phase''. The expansion of the inner region at t > 0 is connected to the outer envelope of the now ionized cloud core through this shock whose strength is an increasing function of the exponent n. We also discuss the evolution of the strong stellar winds of massive stars inside these champagne flows.
