Pole coordinates and shape of 30 asteroids

Astronomy and Astrophysics Supplement Series, Sep 1998

To obtain a statistically reliable sample of minor planets with known rotation axis orientation and axes ratios, a selection of photometric lightcurves sufficiently 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 plot catalogue of asteroids

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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)


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C. Blanco, D. Riccioli. Pole coordinates and shape of 30 asteroids, Astronomy and Astrophysics Supplement Series, 1998, pp. 385-394, Volume 131, Issue 3, DOI: 10.1051/aas:1998277