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H.W. Yorke (Jet Propulsion Laboratory, California Institute of Technology), S. Richling (Institute for Theoretical Astrophysics, Univ. Heidelberg)
The hydrodynamic evolution of protostellar disks under the influence of external ultraviolet radiation and stellar winds from their central stars is calculated numerically with a 2D (rotational symmetry assumed), multigrid code. The UV radiation alone results in the gradual photoevaporation of the disk, characterized by a neutral disk wind (disk material dissociatiated and heated by FUV radiation) surrounded by an ionization front, where the outflowing disk wind is ionized by EUV radiation. The overall appearance resembles the cometary shape of "proplyds" seen in Orion, NGC3603, and other star forming regions containing O stars. When the disk's central star has a T Tauri type wind, however, the shape and appearance will be modified. The stellar wind, assumed to be initially isotropic, is focussed into a bipolar outflow. Mixing of the stellar wind containing no angular momentum with molecular material from the inner disk regions, moving at Keplerian velocities, results in an outflow that has too much angular momentum to remain strongly focussed. Thus, the axial regions of the outflow are depleted of material and the corresponding temperatures are low due to adiabatic expansion. Most of the outflowing material is concentrated in a conical shell, the opening angle of which is determined by the parameters of the disk wind.
This research is supported by NASA through grant NRA-99-01-ATP-065 and by the DFG (Deutsche Forschungsgemeinschaft).
The author(s) of this abstract have provided an email address for comments about the abstract: Harold.Yorke@jpl.nasa.gov