Pole coordinates and shape of 30 asteroids
Astron. Astrophys. Suppl. Ser.
Pole coordinates and shape of 30 asteroids
C. Blanco 0
D. Riccioli 0
0 Institute of Astronomy, University of Catania , Viale A. Doria 6, 95125 Catania , Italy
To obtain a statistically reliable sample of minor planets with known rotation axis orientation and axes ratios, a selection of photometric lightcurves su ciently covered to give the elements needed for applying the computation methods of the rotational elements was made. Using the data reported in the \Amplitude-longitude (A − ) plot catalogue of asteroids" (Riccioli & Blanco 1995) as a starting point, the amplitude-magnitude (AM ) method (Zappala et al. 1983a) was adopted. Due to the poor data available, it was possible to apply the (AM ) method only to 30 asteroids. For more than half of these objects no previous determination of pole coordinates and shape exists in the literature.
asteroids
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
quali ed 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
(Zappala
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 − ), 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 rst determination of the rotation axis
orientation and shape.
2. Photoelectric observations and reduction
To increase the observational data contained in the
literature, mainly in the \Asteroid Photometric
Catalogue"
(Lagerkivst et al. 1987a)
and its Updates
(Lagerkvist et al. 1989, 1992)
, a long-term and intense
photoelectric observational campaign was undertaken in
collaboration with M. Di Martino and G. De Sanctis of
Torino Astronomical Observatory. Besides the purpose of
building lightcurves of the asteroids with observational
constraints
(Di Martino et al. 1994)
, its aim is to observe
asteroids with few or incomplete lightcurves, preferably
at suitable ecliptic longitudes to obtain (A − ) plots with
well distributed points in longitude.
The photoelectric observations, still in progress,
have been carried out, since March 1992, with the
91-cm Cassegrain telescope at M.G. Fracastoro station
of Catania Astrophysical Observatory (since 28 October
1995 this has been the new name of Serra La Nave stellar
station of Catania Astrophysical Observatory). In Table 1
of the \Amplitude-longitude (A − ) plot catalogue of
asteroids"
(Riccioli & Blanco 1995)
, the date of the
observational runs and the name of the observed asteroids
are reported.
During the 23 runs of observations already made, each
lasting on average ten nights, we have used the same
instrumentation (photomultiplier, diaphragm, lters,
etc...) and observing strategy
(Di Martino et al. 1994)
.
The transformation to the standard system was made by
means of groups of standard stars, taken from Blanco
et al. (1968) and
Landolt (1973)
, usually observed every
night on their passage at the meridian. Further
information on the reduction and plotting procedure are reported
in Di Martino et al. (1994).
3. Pole and shape determination
A( )
phase angle, by means of (...truncated)