摘要：Aims. We investigated 1234 fundamental mode RR Lyrae stars observed by
the All Sky Automated Survey (ASAS) to identify the Blazhko (BL) effect. A sample of 1547
BL stars from the literature was collected to compare the modulation-period distribution
with stars newly identified in our sample.
Methods. A classical frequency spectra analysis was performed using
Period04 software. Data points from each star from the ASAS database were
analysed individually to avoid confusion with artificial peaks and aliases. Statistical
methods were used in the investigation of the modulation-period distribution.
Results. Altogether we identified 87 BL stars (48 new detections), 7
candidate stars, and 22 stars showing long-term period variations. The distribution of
modulation periods of newly identified BL stars corresponds well to the distribution of
modulation periods of stars located in the Galactic field, Galactic bulge, Large
Magellanic Cloud, and globular cluster M5 collected from the literature. As a very
important by-product of this comparison, we found that pulsation periods of BL stars
follow Gaussian distribution with the mean period of 0.54 ± 0.07 d, while the modulation periods
show log-normal distribution with centre at log (Pm [d]) = 1.78 ± 0.30 dex. This
means that 99.7% of all known modulated stars have BL periods between 7.6 and 478 days. We
discuss the identification of long modulation periods and show, that a significant
percentage of stars showing long-term period variations could be classified as BL
stars.
