Application of the Thin Shock Layer Model to the Determination of the Parameters of the Envelopes of Young Stellar Objects

Classical problems of unsteady one-dimensional and two-dimensional explosive motions are generalized to the case of gas expansion by ionizing ultraviolet radiation in regions of active star formation. An essential feature of the developed model is the use of the ionization balance condition instead of the adiabaticity condition, which is invalid due to the interaction of gas with radiation. The model allows one to study gas dynamic phenomena in an inhomogeneous medium and in a non-stationary radiation field. The results of the calculations are compared with those obtained within the framework of the Cherny and Kompaneets approximations, and a physical interpretation of the differences that arise is given. It is analytically shown that for one-dimensional motions it is impossible to move a finite mass of gas to infinity in a finite time interval. A criterion is derived for such a two-dimensional density distribution in the gas envelope, at which a “break” of the envelope occurs in a finite time. An analysis of theoretically predicted properties of motions at different stages of the evolution of HII regions with observations is carried out. The analysis made it possible to establish new dependencies of the measured fluxes of ultraviolet, infrared and radio radiation on the parameters of the ionized and neutral gas involved in the motion.