Variations in stellar and dust shell radiations with respect to radial distance for low-mass (left panel) and high-mass (right panel) protostellar cores. For r < r_threshold (marked by the vertical dashed-dotted line), the stellar radiation decreases as U(T_*, nodust) ~r⁻². For r > r_threshold, this stellar radiation (U(T_*)) is quickly reduced because of dust attenuation. The radiation in the outer region is mainly dominated by the emission from the dust shell (U(T_shell)).