3 Results

Table 1 lists the program stars and summarizes their most relevant stellar properties taken either from the recent literature or from the second edition of the catalog of Chromospherically Active Binary Stars (CABS, Strassmeier et al. [1993]) if appropriate. Table 2 identifies the comparison and the check stars, the observing interval, whether a neutral density filter was needed or not, the useable number of differential data points - each the mean of three readings on the variable and the comparison -, and which telescope was used.

3.1 Seasonal light curves

The individual panels in Fig. 1 through Fig. 45 present the photometric data in one bandpass (usually V or y), the periodogram from these data, and the phased seasonal light curve from the best-fit period. We emphasize that the sometimes abnormally large scatter in the phase plots is almost exclusively due to intrinsic spot changes and not due to instrumental scatter.

Figure 1: The y-light variations of HR 5B in 1996/97 (left panel). The right panel is the periodogram showing the adopted significance level at a signal-to-noise ratio of 4 according to the criteria of Breger et al. ([1993]). No clear period was found for HR 5. For individual comments and discussions, see Sect. 4

Figure 2: LN Peg (=SAO 91772). The right panel shows the phased light curve from the best-fit period listed in Table 1. The corresponding frequency peak is indicated in the header of the plot along with the Fourier (half) amplitude and the phase shift from time T0=0. Note that the phase plots show the combined data from the entire observing season and its scatter is usually due to intrinsic amplitude changes

3.2 Photometric periods

Table 1 includes the results from our period analysis. We applied a menu-driven program that performs a multiple frequency search through Fourier transforms with a non-linear least-squares minimization of the residuals (Sperl [1998]). The Fourier search range included a large number of frequencies up to the Nyquist frequency with a frequency spacing optimized for each individual data set. In most situations the frequency with the highest amplitude was adopted but in some cases, e.g. when the light curve appeared double humped, $f = 2 \ f_{\rm highest}$ was used. The best fits are determined by minimizing the squares of the residuals between trial fits and measurements, and is done with program curfit (Bevington [1969]). The function that is fit to the data is

$$m(t) = A_{\rm0} + \sum_{i=1}^{7} \ A_{i} \sin (2 \pi f_{i} + 2 \pi \phi_{ i})$$ (1)

where m(t) is the predicted magnitude, $A_{\rm0}$ is the magnitude zeropoint and is subtracted prior to minimization, A _i are the amplitudes for each frequency (half of the peak-to-peak light curve amplitudes), f _i are the frequencies, and $\phi_i$ is the phase given in units from 0 to 1. Note that i=7 is the maximum number of simultaneous frequencies for the least-squares minimization. In our case, a single frequency (i=1) was sufficient for all data sets and is physically plausible.

To judge the significance of certain frequency peaks we overplot a running mean of the frequency distribution for a signal-to-noise (S/N) ratio of 4:1 which was found empirically by Breger et al. ([1993]). From numerical simulations with varying amounts of white noise, it was shown by Kuschnig et al. ([1997]) that frequency peaks with $S/N\geq4.0$ suggest a 99.9% probability for a real period. Individual errors are estimated from the width of the frequency peak at $\chi^2_{\rm min} + \chi^2_{\rm min}/(n-m)$ where n is the number of data points and m the number of parameters (n  -  m is then the number of the degrees of freedom; m=4 in our case). For details we refer to Bevington ([1969]).

The periods designated $P_{\rm phtm}$ in Table 1 are the average photometric periods computed from the individual bandpasses and are always given up to the last significant digit. The light curves in the figures are phased with these periods unless otherwise noted. The corresponding zero point in time is T₀=0 for all light curves. The phase shift of the light-curve maximum with respect to T₀ is indicated in the upper right corner of each phase-curve panel in Figs. 1-45. A slight shift between light curves for the same star but from different telescopes is due to slight differences in the separately obtained periods.

Table 1 also contains a column for the stellar radius that is computed from the value of $v\sin i$, the latter taken from the literature, and our photometric period.