The Panel a) shows the original spectra of S4, S7, S8, S21 and S23 before UV irradiation while the panel b) shows the spectra of S4, S7, S8, S21 and S23 after UV irradiation. In panel c), the interstellar extinction curves of DISM (Fitzpatrick 1999) and the average galactic extinction curve, as well as for the objects HD 698, HD 3191, NGC 457 Pesch9 and Cr 463-5 (Fitzpatrick & Massa 2007) are shown. The curves labeled P5 in panel b) are the extracted UV bump profiles around 4.6 μm^-1.