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Up: Pole coordinates and shape


1 Introduction

The availability of a statistically reliable sample of asteroids with well-determined rotation axis orientation and axes ratios is essential for the statistical and theoretical modelling of their collisional evolution. The knowledge of the rotation axis distribution becomes more interesting in the case of the asteroid families, because it is possible to ascertain how the fragments of the parent body are distributed in space upon fragmentation. For these reasons, in the last years some parts of observational asteroid researches have been focused on the collection of photometric lightcurves with the aim of acquiring enough and qualified data to compute the pole coordinates and shape of the asteroids.
A long-term and intense photoelectric observational campaign is in progress at the Astronomy Institute of Catania University, in collaboration with Torino Astronomical Observatory, having as its main aim the integration of the observational data of the asteroids with few or incomplete lightcurves.
By means of a careful search in the literature for asteroid lightcurves and of those recorded in our observational campaign, an amplitude-longitude plot catalogue of asteroids was compiled (Riccioli & Blanco 1995). Using the data reported in this catalogue as a starting point, we utilized the amplitude-magnitude (AM) method (Zappalà et al. 1983a) based on the assumption of triaxial ellipsoid shape of the asteroid, rotating around the shorter axis. From the lightcurves, we obtain the magnitude V at the maximum of the lightcurve and the amplitude A, depending on the rotation axis orientation and on the shape of the asteroid, respectively. The ratio between the two greater axes of the approximating ellipsoid can be obtained from the plot $(A-\lambda)$, if we have a continuous and good distribution in longitude of the observed amplitudes.
Due to the scarce availability of lightcurves from which the amplitude at suitable longitudes can be obtained, it was possible to apply the (AM) method only to 30 asteroids. Of these objects we report the observed and theoretical amplitude-longitude plots and the found values of the pole coordinates and of the axes ratios. For more than half the objects, this is the first determination of the rotation axis orientation and shape.



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Up: Pole coordinates and shape

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