We are thankful to V.P. Grinin who initiated this work, A.G. Kritsuk for consideration of the thermal balance of gas, S.I. Grachev for helpful discussions, and J. Gürtler for suggestions improved the text. Special thanks to Claude Catala, the referee, for many valuable comments and for sending the unpublished results. V.B.I. acknowledges the support from the Alexander von Humboldt Foundation. The work was partly supported by the ESO C&EE Programme (grant A-01-093).
© European Southern Observatory (ESO) 1997
Online publication: June 5, 1998