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Astron. Astrophys. 327, 317-324

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Photoevaporation of protostellar disks

II. The importance of UV dust properties and ionizing flux

Sabine Richling and Harold W. Yorke

Astronomisches Institut der Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
(email: richling@astro.uni-wuerzburg.de, yorke@astro.uni-wuerzburg.de)

Received 13 March 1997 / Accepted 27 May 1997


We study the hydrodynamic evolution of protostellar disks under the influence of a central source of ionizing radiation and its stellar wind. Here we examine the effects of an important contribution to the diffuse radiation field - the scattering of hydrogen-ionizing photons on dust grains (dust scattering). We present and discuss the resulting changes in the evolution of the system under a variety of conditions both with and without dust scattering. An important consequence is the significant increase in the photoevaporation rate. Depending on the scattering coefficient assumed, the presence of dust within the ionized region can increase the density and flow of ionized material and correspondingly shorten the disk's lifetime by a factor of two or more. In addition, the temperature of the ionized outflowing gas is slightly higher and remains more nearly constant over the extent of the ionized region, even in the regions shadowed from direct stellar radiation.

We also investigate the influence of other major parameters of the problem, wind velocity, wind mass loss rate, and stellar ionizing flux, by systematically varying these parameters. Over a large range of values of stellar ionizing flux FORMULA we find a power law dependence of the disk mass loss rate due to photoionization FORMULA which is comparable to analytic estimates. Deviations from this power law occurred for moderate values FORMULA s-1 due to our finite disk size and for low values FORMULA s-1 due to the resulting non-steady flow pattern. Because we have assumed a warm (FORMULA K) wind and have included heating, cooling, ionization, and recombination processes in the stellar wind, we find that the disk's photoevaporation rate depends on the assumed wind parameters in a manner which can be explained by the loss of UV ionizing photons very close to the central star.

Key words: radiation transfer - stars: circumstellar matter - stars: formation of - ISM: jets and outflows - HII regions

Send offprint requests to: S. Richling

© European Southern Observatory (ESO) 1997

Online publication: October 1, 1997
Last change: April 8, 1998