Period04: A software package to extract multiple frequencies from real data

Period04, a reworked and extended version of Period98 (Sperl 1998) and PERIOD/ PERDET (Breger 1990), is a new software package especially dedicated to the statistical analysis of large astronomical data sets containing gaps. It offers tools to extract the individual frequencies from the multiperiodic content of time series and provides a flexible interface to perform multiple-frequency fits. A review of the functions of Period04 is given.