Up: Pole coordinates and shape
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 , 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.
Up: Pole coordinates and shape
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