Gamma Doradus : evidence for a new class of pulsating star.

We present further photometric observations of the peculiar F-type dwarf y Doradus. The two periodicities discovered previously are still present and phase-locked. In addition, there is marginal evidence for a third period not present in previous data. The hypothesis that the star is singly periodic with a double-wave light curve is shown to be untenable. The light variations are modelled by two starspots in differential rotation. The large size of the spots and the high stability of their periods count against this hypothesis. We conclude that the most plausible cause of the light and line-profile variations is lowdegree g-mode non-radial pulsation. This star is the best example of what appears to be a new class of pulsating F-type variable. The light variations cannot be fully accounted for by two periods; the nature of the aperiodic component is briefly discussed. Key words: stars: individual: y Dor - stars: oscillations - stars: variables: other.