Formation of bipolar flow within a plane-parallel gas layer by stellar wind

The unsteady flow induced by a spherical stellar wind immersed in a plane-parallel interstellar cloud, which is in hydrostatic equilibrium due to self-gravity, is investigated. It is shown that the interaction of the stellar wind with an inhomogeneous cloud leads to the formation of a compressed shell which is elongated in the direction perpendicular to the plane of the ambient cloud. After the shock front propagates a few scale heights of the ambient cloud, the compressed shell becomes bipolar in shape. The kinetic energy of the shell relative to the internal energy increases during the propagation of the shock front due to the density gradient of the ambient cloud. The shell driven by the pressure of the stellar wind (energy driven) and the ambient cloud supported by turbulent pressure reproduce well the dynamical properties of the bipolar flow. The dissociation of molecules by the shock front is examined, and it is shown that most of the gas in the shell may remain in a molecular state. (author)