The group of pulsating CP2-stars (also called “rapidly oscillating Ap stars” provides asteroseismology with oscillation spectra of high accuracy. The potential as a diagnostic tool for modelling stellar interiors is widely appreciated. The identification of pulsation modes is important for such an analysis. However, this is rarely possible in an unambiguous manner. To improve the situation and to make use of additional information, we observed HD 128898 simultaneously spectroscopically and photometrically at ESO. For each of our individual CAT-CES spectra (1 minute integration time) it was thus possible to determine the pulsation phase at mid-exposure. A total of 887 spectra (R = 50000) were binned according to their pulsation phase and coadded to improve significantly the signal to noise ratio.