Abstract

The Observation of the Asteroidal Occultation of 39 Laetitia on March 21, 1998

Roberto Di Luca, Carlo Frisoni
Presented by Carlo Frisoni

Die Beobachtung von Sternbedeckungen durch Kleinplaneten werden durch ungenaue Vorhersagen erschwert. Nicht so beim Ereignis vom 21. März 1998.
Das Laetitia-Ereignis wird hoffentlich das erste einer neuen Serie gleichartiger Beobachtungen sein, bei denen genaue Vorhersagen es erlauben, sich auf wenige, sorgfältig ausgewählte Bedeckungen, die auf der Basis einer hohen Erfolgswahrscheinlichkeit beruhen, zu konzentrieren.

Occultations of stars by asteroids are events normally very difficult to observe successfully, because of the high uncertainty usually afflicting predictions. This was not the case of the occultation of PPM 121913 by the asteroid 39 Laetitia, on March 21 1998 when it was possible to co-ordinate with good results a team of italian amateur astronomers of IOTA-ES and UAI so that most of the observers observed the occultation. Gathering the several other European observations (Spain, France), that resulted in very good agreement with those of the italian team, we can draw the following conclusions:

• the occultation gave the best result ever obtained in Europe;
• for the first time in Italy most observers decided their observing site on the basis of a team strategy;
• for the first time in Europe it was possible to reconstruct the detailed projected profile of an asteroid, measuring with precision the lengths of two axis and improving the data previously obtained by photometric estimates;
• this allowed also to select among the most probable shape of the asteroid: a sort of almost round loaf squashed on one axis.
• Analysis of the observations supports the hypothesis that the material on the surface of 39 Laetitia may be darker than expected.

Table 1: Complete list of observers

The Laetitia event will hopefully be the first of a new series of similar observations, in which accurate predictions allow concentrating the observational efforts on a few events carefully selected on the basis of a reasonable chance of success.

Dr. Carlo Frisoni, UAI (Unione Astrofili Italiani) and AAB (Associazione Astrofili Bolognesi)
Address: Via G.Sozzi 6, Casalecchio di Reno, Italia
Telephone: +39 5 1591518

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