DISCOVERY OF ADDITIONAL PULSATION MODES IN AI VELORUM

We analyse 13 394 blue-light photometric observations of the high-amplitude-delta-Scuti star AI Velorum. These data were obtained for six seasons spanning 38 years. We find that in addition to the well-known fundamental and first-overtone radial modes, two previously undiscovered periodicities are present; one of them was initially suspected by Walraven many years ago. These periodicities are present in every season. A tentative identification in terms of the third and fifth radial overtones is proposed. A non-linear interaction term between one of the new periodicities and the first overtone is present. A fifth mode, intermediate in period between the fundamental and first overtone may also be present. We also find that the period of the first overtone is increasing at a steady rate, but that there is little or no change in the period of the fundamental mode over an interval of more than 50 years.