2000A&AS..142....1P

A comprehensive frequency analysis of 57 Tau, supposed only a static pulsational arrangement, is presented based on 54 nights of photometric data collected between 1981 and 1995 (althogether 232 hours). The presence of individual frequencies is confirmed by intercomparing four subsets of this data set, however, the uncertainties in data coming from the sparse nights and low signal weaken the conclusion on some results. The entire data base is then used to resolve closely spaced peaks. Twelve frequencies are indentified using this process. Further multisite observations are recommended to confirm the present frequency solution. Two periods, with a high probability of being real, are found in the low frequency domain. They are suggested to arise from binarity or g modes, as in γ Dor stars. Single unusual cycles, possessing large amplitude, or displaying asymmetry, have been localized. A coherent frequency at 29.83c/d with variable amplitude was found. The nonstandard behaviour of the light variation indicates that nonlinear and/or nonstationary processes could be very important in the investigation of δ Scuti observations.