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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.
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