Nonlinear Dynamical Analysis of Stellar Variability
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**Session 84 -- Variable Stars**
*Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)*

## [84.03] Nonlinear Dynamical Analysis of Stellar Variability

*A. S. Sharma (U.Maryland)*
Earlier attempts in characterising the irregularities in stellar
pulsations as arising from chaotic dynamics have been inconclusive due
mainly to the short data lengths and high noise levels. Pulsating white
dwarfs have been recognized to be suitable candidates for the study of
dynamical behavior because of their short pulsation time scales,
allowing a typical observation to cover a significant number of periods.
A major reason of the inconclusive result of the earlier studies is the
short data length due to the finite observation time of 3-4 hours with a
single telescope. With pulsation periods of 3-12 min, a typical
observation covers about forty periods, which may not be adequate to
yield its complex behavior. However, the Whole Earth Telescope has
produced more than 264 hrs of nearly continuous time-series photometry
data on the pulsating pre-white dwarf star (DOV) PG 1159--035,
consisting of more than 50,000 data points. A singular spectrum analysis
of the time series light curve data yields two dominant
eigenvalues close to each other. The rest of the eigenvalues however
does not define a single noise floor but many of them, although with
small values, are above an average noise floor. This suggests that the
dynamics of PG 1159--035 is governed by two sets of variables: the two
dominant ones and some others which are not strongly coupled to these
two but may be strongly coupled among themselves. The potentially low
dimensional dynamical behavior is further studied by computing the
correlation dimension and the reconstruction of phase space.

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