extinction curve taken from @cardelli89 with $R_V=3.1$. Thus, the extinction at any wavelength $\lambda$, $A_\lambda$ (in units of magnitude), can be determined if we set a value of $A_V$ (extinction at $V$ band). The optical depth can be related with the extinction as $\tau_\lambda =A_V/1.086$. The following results does not change drastically if we assume an extinction curve appropriate for the Large Magellanic Clouds (LMC) or the Small Magellanic Cloud (SMC), since the detailed shape of UV–optical SED is not important in this paper. Strictly speaking, we treat scattering as effective absorption, and this treatment would overestimate the absorbed energy. Thus, we interpret $A_V$ given here as effective absorption optical depth, so that the total energy absorbed by dust in our formulation is equal to the energy that would be absorbed if scattering were properly treated.

@galliano03 also adopted a similar treatment, which is valid if dust is distributed in a thin shell surrounding the stars. Such a “screen” geometry enhances the effect of dust extinction (i.e., radiative transfer) in comparison with a mixed geometry between stars and dust. Thus, our models are suitable to examine the extent to which the radiative transfer effects could affect the FIR SEDs.

Grain 