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N. Jevtic (NAMS, Richard Stockton College), E. O. Waagen (AAVSO), J.S. Schweitzer (University of Connecticut)
There have been recent reports of evidence for low-dimensional chaos in a number of semiregular variables, RS Cyg among them (ApJ, 2004, 613, Issue 1, pp. 532-547). The data analyzed for RS Cyg in that study was its photometric light curve, sampled at 10-day intervals, that was 15 cycles long (6,255) days. We analyze a daily-averaged light curve from the AAVSO International Database 11,749 days long (~double the length and ten times the coverage) chosen for its continuity. With the 10-times greater sampling rate on almost twice the data, the wavelet method yields additional harmonics of the fundamental. We show that a two-dimensional single-oscillation nonlinear system, when stochastic fluctuations are included, can exhibit similar behavior of a ``comb" of frequencies in the power spectrum. Moreover, the reported Broomhead-King projections of a curve wrapped around a torus are typical for quasiperiodic systems with a fundamental and a first harmonic. Using the Hurst coefficient, we identify two distinct sections in the RS Cyg data. While the entire data set is slightly anti-persistent, one of the two sections has a Hurst coefficient that indicates persistent behavior while the other is strongly anti-persistent. The latter is in contrast with the behavior of other variables that have been reported to be chaotic and since anti-persistent behavior is considered rare in nature, RS Cyg will be the topic of further study.
The author(s) of this abstract have provided an email address for comments about the abstract: nada.jevtic@stockton.edu
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.