Penetration and circulation currents in irradiated spherically symmetric stellar atmospheres

The motions driven in a stellar atmosphere by heating from a companion in a close binary system are investigated. Earlier work is extended by considering a spherical atmosphere in such a way as to be able to investigate the penetration of the motions into the unilluminated part of the star. It is assumed that the incident radiation is a monodirectional beam. Even though this beam does not penetrate directly to the dark side of the star except in a very narrow region at the limb, radiative equilibrium is restored only gradually and the circulation currents are found to persist up to approximately 16 deg into the shadow region. Even though the flow speeds are found to be exceptionally large, it is argued that the inclusion of inertial terms, or of turbulence, would reduce them to reasonable values. The quantity of energy carried by circulation into the dark side is estimated, and the results are found to corroborate the view that enough energy can be carried to explain the light curve of HZ Herculis.