PEGASE time evolution of SEDs for [Fe/H] = −2 and a representative initial stellar mass of 10⁷ M_⊙ as if it is at a distance of 10 pc. Since we assume that the star formation lasts for 5 Myr, we start with the SED at 6 Myr to avoid overlapping of lines. Left panel: the evolution for the MKDP IMF. Right panel: the evolution for the CAN IMF. The region below a wavelength of ≈ 1000 Å (marked by arrow and question mark) is the black-body approximation. The PEGASE code does not predict values in this region. More details are given in the text.