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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.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.