NONLINEAR-ANALYSIS OF THE LIGHT-CURVE OF THE VARIABLE-STAR R-SCUTI

It is first shown that the observational light curve data of R Scuti, a star of the RV Tau type, is not multiperiodic and that it cannot hav e been generated by a linear stochastic (AR) process. By default, the signal must be a manifestation of deterministic chaos. We use a novel nonlinear time series analysis, the global flow reconstruction techniq ue, to probe the properties of the irregular pulsation cycles. We show in particular that the chaotic dynamics of this star's complicated li ght curve is captured by a simple four-dimensional polynomial map or f low (four first-order ordinary differential equations). Another import ant feature is that the method allows us to quantify an irregular sign al that has the potential benefit for extracting novel stellar constra ints from an irregular light curve. Finally, from the low dimensionali ty (four) of the flow we can infer a simple physical picture of the pu lsations, and arguments are presented that the pulsations of R Sct are the result of the nonlinear interaction of two vibrational normal mod es of the star.