Variable central stars of young Planetary Nebulae - A photometric study ofthe central star of M 2-54

We acquired 63.8 hours of time-series photometry of the variable central st ar of the young Planetary Nebula M 2-54. This object exhibits light variati ons with a peak-to-peak amplitude of up to 0.3 mag in Johnson V. Two differ ent time scales (several days and several hours) are present. While the lon g-term variations appear to be nonperiodic, the short-term modulations are (quasi)periodic with a time scale of either 8.9 or 14.3 hours. An analysis of the HIPPARCOS photometry of this object did not allow us to infer which of these two time scales is the correct one. The possible causes for the observed variability are examined.. The slow va riations can be explained by either a spot hypothesis or variations in the stellar mass loss; while the short-term modulations are most consistent wit h stellar pulsation. All this behaviour is strikingly similar to that of be st studied representative of this class of variable star, the central star of IC 418, strongly suggesting that the physical cause of the variability o f these two objects is the same. While it appears quite attractive to suspect that we are in the presence of a new class of pulsating variables, further work is needed to confirm or r eject this. Consequently, some suggestions in this direction are given.