at $10^5$ km altitude as a function of input stellar X-ray flux. *Middle-panel:* outward hydrodynamic particle fluxes of oxygen and hydrogen atoms (including those contained in molecules and ions), with the solid lines and circles showing the simulation results and the dotted red line showing half the hydrogen flux, indicating the oxygen loss rate expected if the dissociation products of H$_2$O were lost with the same efficiency. *Lower-panel:* fractionation factors for H and D, $f_\mathrm{H,D}$, and for H and O, $f_\mathrm{H,O}$, as a function of the mass flux. In all panels, the circles show the results of individual simulations []{data-label="fig:MdotgridFx"}](MfluxFxGridlog.pdf "fig:"){width="43.00000%"} ![ *Upper-panel:* outward hydrodynamic mass flux at $10^5$ km altitude as a function of input stellar X-ray flux. *Middle-panel:* outward hydrodynamic particle fluxes of oxygen and hydrogen atoms (including those contained in molecules and ions), with the solid lines and circles showing the simulation results and the dotted red line showing half the hydrogen flux, indicating the oxygen loss rate expected if the dissociation products of H$_2$O were lost with the same efficiency. *Lower-panel:* fractionation factors for H and D, $f_\mathrm{H,D}$, and for H and O, $f_\mathrm{H,O}$, as a function of the mass flux. In all panels, the circles 