**DPS Pasadena Meeting 2000, 23-27 October 2000**

*Session 8. Asteroid Posters I - Physical Studies*

Displayed, 1:00pm, Monday - 1:00pm, Friday, Highlighted Tuesday and Thursday, 3:30-6:30pm, C101-C105, C211
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## [8.08] The Diagnosis of Complex Rotation in the Lightcurve of 4179~Toutatis

*B.E.A. Mueller, M.J.S. Belton, N.H. Samarasinha (NOAO)*

We revisit the visible lightcurve data on 4179~Toutatis
(Spencer *et al.* 1995) to recover the signature of its
excited spin state with an application of our Fourier
transform and WindowCLEAN algorithms (Roberts *et al.*
1987, Belton 1991). WindowCLEAN yields clear and precise
signatures of periodicities associated with the precession
of the long axis about the total angular momentum vector
(0.135 ±0.008\,dy^{-1}, 0.271 ±0.008\,dy^{-1})
and the *combination* of precession and rotation (LAM
state), or oscillation (SAM state), about the long axis
(0.643 ±0.008\,dy^{-1}). These periodicities are
effectively the same as those found in the *model*
calculations of Kryszczynska *et al.* (1999). For an
assumed LAM state, our periodicities yield a mean long axis
precession period P_{\phi} = 7.41 ±0.4\,dy and a
period of rotation around the long axis of P_{\psi} =
5.38 ±0.5\,dy which compares well with the values of
7.35\,dy and 5.41\,dy found in the analysis of radar
data (Hudson and Ostro 1995).

We explain why the dramatic change in the Earth-Toutatis-sun
geometry during the time that the lightcurve was obtained,
and which we had originally thought would undermine the
derivation of 4179~Toutatis periods by Fourier analysis, has
little effect on the results obtained.

Using the 4179~Toutatis example as a guide we discuss
limitations on deriving information about complex spin
states from asteroidal light curves.

This work is supported by a Planetary Astronomy Grant from
NASA.

References:

Belton, M.J.S., 1991. In *Comets in the
Post-Halley Era* **2**, Eds.\ R.L. Newburn Jr. and J.
Rahe. Kluwer Academic Publishers. pp. 691-721.

Hudson, R.S. and S.J. Ostro 1995. *Science*
**270**, 84-86.

Kryszczynska, A., T. Kwiatkowski, S. Breiter,
and T. Michalowski 1999. *Astron. Astrophys.* **
345**, 643-645.

Spencer, J.R. *et al.* 1995. *Icarus* **
117**, 71-89.

Roberts, D.H., J. Lehar, and J.W. Dreher 1987.
*Astron. J.* **93**, 968-989.

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