Mid-IR Spitzer photometry of two YSOs fitted using YSO models (Robitaille et al. 2007). The filled circles represent the input fluxes. The black curve shows the best fit, while the gray curves display subsequent good fits. The dashed curve shows the stellar photosphere corresponding to the central source of the best-fitting model, as it would look in the absence of circumstellar dust (but including interstellar extinction). Upper panel: SED fit of N191-YSO1. The stellar mass according to these models varies between 16 and 21 M_⊙. The best fit is for a 20 M_⊙ protostar with a derived total luminosity of 2.9  ×  10⁴ L_⊙. Lower panel: SED fit of N77-YSO1. The stellar mass according to these models varies between 10 and 17 M_⊙. Note that the lack of JHK photometry leads to a wider range of selected models. The best fit is for a 10 M_⊙ protostar with a derived total luminosity of 1.0  ×  10⁴ L_⊙.