1997A&A...321..145S

Based on new observations, it is shown here that the amplitude of one of the three well known and stable short periods in the β Cep variable 16 Lac has changed: while the radial mode P₁=0.16917d is near its lower amplitude level and the amplitude variation of the non-radial mode P₃=0.18173d is still probably in phase with the orbital period, the amplitude of the NR mode P₂=0.17077d has increased progressively by a factor two in the last ten years. The observed phase of P₂ shows that at least for this period, the previous ephemeris is no longer valid. Various hypotheses are proposed to account for the observed amplitudes variations.