3 Data analysis

A multiple-frequency analysis of DQ Cephei was performed with a package of computer programs employing single frequency (Fourier) and multiple-frequency least-squares techniques (program PERIOD, Breger 1990) which utilize Fourier as well as multiple-least squares algorithms. The latter technique fits a number of simultaneous sinusoidal variations in the magnitude domain and does not rely on prewhitening.

Power spectra obtained from the frequency analysis clearly show the existence of two pulsation frequencies (12.6826 cycle per day and 8.0480 cycle per day) (see Fig. 1). A third peak (1.3488 cycle per day) which is a little above the noise level can be picked up too. After removal of the first, second and third frequencies, the residuals are of the order of 0.013, 0.009 and 0.008 mmag respectively. The three-frequency solution to the data is given in Table 2 and its fits to the data are displayed in Fig. 2. Comparing the power spectrum with the previous one (Pena 1983) (see Fig. 1), we find that the second peak (8.0480 cycle per day) has become significantly larger than in previous observations.

  

Figure 1: The power spectra for the data observed in 1981 and 1997

  

Figure 2: The fit of the three-frequencies solution to the observations (1997)

  

Table 2: Component frequencies and amplitudes for DQ Cephei