Photospheric Stellar Activity Cycles

Details Photospheric Stellar Activity Cycles Photospheric Stellar Activity Cycles

Aug 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd...8e..55o&link_type=abstract

Solar and Stellar Activity Cycles, 26th meeting of the IAU, Joint Discussion 8, 17-18 August 2006, Prague, Czech Republic, JD08,

Computer Science

Scientific paper

The photosperic solar activity cycles, like the ~11 years long Schwabe and the ~80 years long Gleissberg cycles, as the sunspot data reveal, are continuously changing in time, e.g., the Gleissberg cycle is getting steadily longer during the last few hundred years. Activity cycles, sometimes multiple cycles, are derived for several active stars, from long-term photometric data. The resulting cycle lengths are usually just "quasiperiods", with high scatter around the mean period values, or are just marginal detections. The reason of these results well could be that the cycle periods are not stable but changing in time like on the Sun. To find such changes, however, very long uninterrupted datasets are necessary. We show results of analysing long-term datasets which are compiled from archival photographic and continuous photoelectric observations, using a time-frequency analysis program package (TiFrAn). All cycle periods, even marginal detections that were derived earlier for the studied active stars, are confirmed. However, it is shown that most of the cycle lengths are varying in time, which makes the detection problematic with conventional methods, like the simple periodogram analysis. The results of varying cycle lengths can give observational constraints for the fast developing dynamo theories and calculations.

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