We provide simple polynomial fits to the X-ray photoelectric cross-sections
(0.03 < E < 10keV) for mixtures of gas and dust found in protoplanetary disks.
Using the solar elemental abundances of Asplund et al. (2009) we treat the gas
and dust components separately, facilitating the further exploration
evolutionary processes such as grain settling and gain growth. We find that
blanketing due to advanced grain-growth (a_max > 1 micron) can reduce the X-ray
opacity of dust appreciably at E_X ~ 1keV, coincident with the peak of typical
T Tauri X-ray spectra. However, the reduction of dust opacity by dust settling,
which is known to occur in protoplanetary disks, is probably a more significant
effect. The absorption of 1-10keV X-rays is dominated by gas opacity once the
dust abundance has been reduced to about 1% of its diffuse interstellar value.
The gas disk establishes a floor to the opacity at which point X-ray transport
becomes insensitive to further dust evolution. Our choice of fitting function
follows that of Morrison & McCammon (1983), providing a degree of
backward-compatibility.Comment: 34 pages, 7 figures. To be published in in Ap
