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Published online by Cambridge University Press: 25 May 2016
We present a detailed period analysis for 98 red semiregular variables by means of Fourier and wavelet analysis of long-term visual observations carried out by amateur astronomers. The overwhelming majority of the studied stars show multiperiodic behaviour. We found two significant periods in 62 variables, while there are definite signs of three periods in 13 stars. 20 stars turned out to be monoperiodic with small instabilities in the period. Since this study deals with the general trends, we want to find only the most dominant periods.
The distribution of periods and period ratios is examined in the (log P1, log P0/P1) plots. Three significant and two less obvious sequences are present which can be explained as the straight consequence of different pulsational modes. This hypothesis is supported by the multiperiodic variables with three periods. A clear distinction between C-rich and O-rich stars has been found in these diagrams suggesting a connection between the chemistry and pulsational characteristics.