**AAS 199th meeting, Washington, DC, January 2002**

*Session 93. Data Analysis Challenges in Solar Stellar Astrophysics*

Display, Wednesday, January 9, 2002, 9:20am-6:30pm, Exhibit Hall
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## [93.03] Nonlinear Time Series Analysis of White Dwarf Light Curves

*N. Jevtic (Physics Dept., U. Connecticut), S. Zelechoski (U. Connecticut 2001 REU Program, UCSD), H. Feldman (U. Connecticut 2001 REU Program, U. California, Berkeley), C. Peterson, J. Schweitzer (Physics Dept., U. Connecticut)*

We use nonlinear time series analysis methods to examine the
light intensity curves of white dwarf PG1351+489 obtained by
the Whole Earth Telescope (WET). Though these methods were
originally introduced to study chaotic systems, when a clear
signature of determinism is found for the process generating
an observable and it couples the active degrees of freedom
of the system, then the notion of phase space provides a
framework for exploring the system dynamics of nonlinear
systems in general. With a pronounced single frequency, its
harmonics and other frequencies of lower amplitude on a
broadband background, the PG1351 light curve lends itself to
the use of time delay coordinates. Our phase space
reconstruction yields a triangular, toroidal
three-dimensional shape. This differs from earlier results
of a circular toroidal representation. We find a
morphological similarity to a magnetic dynamo model
developed for fast rotators that yields a union of both
results: the circular phase space structure for the
ascending portion of the cycle, and the triangular structure
for the declining portion. The rise and fall of the dynamo
cycle yield both different phase space representations and
different correlation dimensions. Since PG1351 is known to
have no significant fields, these results may stimulate the
observation of light curves of known magnetic white dwarfs
for comparison.

Using other data obtained by the WET, we compare the phase
space reconstruction of DB white dwarf PG1351 with that of
GD 358 which has a more complex power spectrum. We also
compare these results with those for PG1159. There is some
general similarity between the results of the phase space
reconstruction for the DB white dwarfs. As expected, the
difference between the results for the DB white dwarfs and
PG1159 is great.

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