摘要：Context. Large all-sky surveys provide us with a lot of photometric data
that are sparse in time (typically a few measurements per night) and can be potentially
used for the determination of shapes and rotational states of asteroids. The method
generally used to derive these parameters is the light curve inversion. However, for most
asteroids their sparse data are not accurate enough to derive a unique model and the light
curve inversion method is thus not very efficient.
Aims. To fully utilize photometry sparse in time, we developed a new
simplified model and applied it on the data from the Lowell photometric database. Our aim
was to derive spin axis orientations and shape elongations of asteroids and to find out if
there are some differences in distributions of these parameters for selected
subpopulations.
Methods. We modeled asteroids as geometrically scattering triaxial
ellipsoids. Observed values of mean brightness and the dispersion of brightness were
compared with computed values obtained from the parameters of the model, i.e., the
ecliptical longitude λ and latitude β of the pole and the
ratios a/b, b/c of
axes of the ellipsoid. These parameters were optimized to get the best agreement with the
observation.
Results. We found that the distribution of λ for main-belt asteroids
is not uniform and is dependent on the inclination of the orbit. Surprisingly, the
nonuniformity of λ distribution is larger for asteroids residing on
low-inclination orbits. We also studied distributions of a/b for
several groups of asteroids and found that small asteroids (D< 25 km) are on average
more elongated than large ones.
