X-ray irradiated protoplanetary disk atmospheres I: Predicted emission
line spectrum and photoevaporation
release_vb6mojyh3ffdheojm7rbmsb6zy
by
Barbara Ercolano ,
Cathie C. Clarke Institute of Astronomy, University of Cambridge,
2008
Abstract
We present MOCASSIN 2D photoionisation and dust radiative transfer models of
a prototypical T Tauri disk irradiated by X-rays from the young pre-main
sequence star. The calculations demonstrate a layer of hot gas reaching
temperatures of ~10^6 K at small radii and ~10^4 K at a distance of 1 AU. The
gas temperatures decrease sharply with depth, but appear to be completely
decoupled from dust temperatures down to a column depth of ~5*10^21 cm^-2.
We predict that several fine-structure and forbidden lines of heavy elements,
as well as recombination lines of hydrogen and helium, should be observable
with current and future instrumentation, although optical lines may be
smothered by the stellar spectrum. Predicted line luminosities are given for
the the brightest collisionally excited lines (down to ~10^-8L_sun, and for
recombination transitions from several levels of HI and HeI.
The mass loss rate due to X-ray photoevaporation estimated from our models is
of the order of 10^-8 M_sun yr^-1, implying a dispersal timescale of a few Myr
for a disk of mass 0.027 M_sun, which is the mass of the disk structure model
we employed. We discuss the limitations of our model and highlight the need for
further calculations that should include the simultaneous solution of the 2D
radiative transfer problem and the 1D hydrostatic equilibrium in the polar
direction.
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