All data
were corrected for dead time, atmospheric extinction
and sky background. In case of
observations during more than one night, we merged the data
prior to a Fourier analysis.
Neither smoothing nor averaging was applied. The differential data
were calculated by subtracting one data set from the other. If
necessary, we interpolated linearly between two data points of the comparison
star for a given time.
The differential data were used to calculate amplitude spectra
with a standard Fourier technique (Deeming 1975; Breger 1990)
up to the Nyquist frequency as shown in Figs. 4 (click here)a to 4 (click here)c.
We have also checked the differential data of both comparison
stars for variations.