SIMBAD references

We investigate the effect of ionizing radiation from massive young stellar objects impinging on their emerging spectral energy distribution. By means of detailed radiative transfer calculations including both the gaseous and dust phase of their surrounding protoplanetary discs we highlight the importance of modelling both phases simultaneously when interpreting observations from such objects. In particular we find that models that only include dust may lead to incorrect conclusions about the inner disc evolution. Furthermore, the omission of gas from models overproduces far-infrared and submillimetre (submm) fluxes with the result that derived dust masses may be underestimated by a factor of 2 in some cases. Finally, free-free emission from the ionized component of gaseous discs causes the slope of the dust emission in the submm and mm regime to appear flatter, resulting in incorrectly modelling the dust properties, with consequences on the derived disc masses, power-law index of the surface density profile and other disc properties.