AMPLITUDE MONITORING OF THE BETA-CEPHEI STAR 16-LACERTAE

Based on new observations, it is shown here that the amplitude of one of the three well known and stable short periods in the beta Cep varia ble 16 Lac has changed: while the radial mode P-1 = 0.16917 d is near its lower amplitude level and the amplitude variation of the non-radia l mode P-3 = 0.18173 d is still probably in phase with the orbital per iod, the amplitude of the NR mode P-2 = 0.17077 d has increased progre ssively by a factor two in the last ten years. The observed phase of P -2 shows that at least for this period, the previous ephemeris is no l onger valid. Various hypotheses are proposed to account for the observ ed amplitudes variations.