Period changes in EI Cephei

Abstract

A new period (P = 8.ͩ 439422) of the eclipsing binary system EI Cephei has been given, which is based on all available times of minima. Periods using Strohmeier's (1958) epoch have also been presented for the observations given by other investigators. Period based on only photoelectric minima comes out to be 8.ͩ439336, which is lesser than the earlier periods given in the literature. O-C diagrams of EI Cephei have been presented for the first time, and period variations have been estimated in different portions of the O-C diagram (Figure 2) of EI Cephei. Strong period changes have occured around the years 1959 and 1965. The total change in period (ΔP/P) ranges from 6.7x10⁻⁵to 4.3x10⁻⁴. Thus, ΔP of the order of 10⁻³ d are present, which fact suggest that strong period variations are present in EI Cephei. However, periods given by various investigators show no systematic trend of period variations. The existence of a third body in the system could not be confirmed.