Hα emission line spectroscopy in NGC 330. On the hybrid model for global oscillations in Be star circumstellar disks

We perform an observational test on global oscillations in Be star circumstellar disks in the metal deficient environment of the SMC. According to the hybrid model of disk oscillations early-type Be stars require an optically thin line force to establish a density wave. The low metallicity in the SMC should therefore diminish or prevent the formation of disk oscillations in early-type Be stars. We present short wavelength range spectra around Hα of 48 Be stars in the young open cluster NGC 330 in the SMC. We find that the fraction of early-type Be stars in NGC 330 which host a global disk oscillation does not differ from the known fraction of Galactic field Be stars. This observational result is in contradiction to the theoretical prediction. We discuss several interpretations and propose a further observational test. Based on observations collected with VLT-Kueyen-FORS2-MXU during the commissioning~1 of FORS2 and the mechanical commissioning of the MXU, operated on Cerro Paranal (Chile) by the European Southern Observatory and the VLT instrument consortium (FORS2).