approximately to the planet’s effective temperature, and a number density of . The mixing ratio of HDO at the lower boundary is , corresponding approximately to the value in the Earth’s oceans (@Eberhardt95) and is typical for values in chondritic meteorites (@Marty16), though since the abundance of deuterium is too small to influence the model, any sufficiently small base HDO mixing ratio could have been chosen. The base number density is mostly arbitrary and experiments with other values have shown that my results are not sensitive to this value as long as it is large enough that all of the absorption of the XUV spectrum takes place within the computational domain. The upper boundary altitude is also arbitrary and only chosen to be far enough from the planet that the hydrodynamic outflow is supersonic within the simulation domain; at this boundary, standard zero-gradient outflow conditions are used.

For the stellar XUV spectra in the wavelength range 1 to 400 nm, I use the method and codes developed for solar mass stars by @Claire12. It is important to use realistic stellar spectra since the shape of a star’s XUV spectrum depends on its activity level: more active stars have hotter coronae 