Secular Changes in the Light Curve of the Short-Period Cepheid EU Tau

Abstract

UBVRI photometry and radial velocity measurements of EU Tau obtained during three weeks in November/December 1987 have been used to (1) confirm the period, P = 2.1025 days, and epoch established by Fernie (1987, P.A.S.P.,99, 1093) and earlier observers, and (2) investigate apparent phase and/or amplitude discrepancies in the light curve first reported by Gieren and Matthews (1987, A.J.,94, 431). Comparison of these new data with photometry collected by different observers covering over two decades suggests that the light curve of EU Tau undergoes short-lived (less than about 2 pulsation cycles) changes which appear to occur with a period of roughly 19 – 21 days. Various possible sources of modulation – including binarity, double-mode beating and nonradial pulsations – are considered and rejected as unsatisfactory.