Multiperiodicity in semiregular variables. I. General properties
Abstract
We present a detailed period analysis for 93 red semiregular variables by means of Fourier and wavelet analyses of longterm visual observations carried out by amateur astronomers. The results of this analysis yield insights into the mode structure of semiregular variables and help to clarify the relationship between them and Mira variables. After collecting all available data from various international databases (AFOEV, VSOLJ, HAA/VSS and AAVSO) we test the accuracy and reliability of data. We compare the averaged and noisefiltered visual light curves with simultaneous photoelectric Vmeasurements, the effect of the length versus the relatively low signaltonoise ratio is illustrated by period analysis of artificial data, while binning effects are tested by comparing results of frequency analyses of the unbinned and averaged light curves. The overwhelming majority of the stars studied show multiperiodic behaviour. We found two significant periods in 44 variables, while there are definite signs of three periods in 12 stars. 29 stars turned out to be monoperiodic with small instabilities in the period. Since this study deals with the general trends, we wanted to find only the most dominant periods. The distribution of periods and period ratios is examined through the use of the (log P_0, log P_1) and (log P_1, log P_0/P_1) plots. Three significant and two less obvious sequences are present which could be explained as the direct consequence of different pulsational modes. This hypothesis is supported by the results for multiperiodic variables with three periods. Finally, these space methods are illustrated by several interesting case studies that show the best examples of different special phenomena such as longterm amplitude modulation, amplitude decrease and mode switching.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 June 1999
 DOI:
 10.48550/arXiv.astroph/9904128
 arXiv:
 arXiv:astroph/9904128
 Bibcode:
 1999A&A...346..542K
 Keywords:

 STARS: OSCILLATIONS;
 STARS: AGB AND POSTAGB;
 STARS: VARIABLES: DELTA SCT;
 Astrophysics
 EPrint:
 16 pages + 15 figures (3 figures oversized), accepted for publication in Astronomy &