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Context: Stellar occultations, greatly enhanced by the publication of theGaia data releases, permit not only the determination of asteroid size andshape, but also the retrieval of additional, accurate astrometry, with apossible relevant impact on the study of dynamical properties. The use of Gaiaas reference catalogue and the recent implementation of an improved error modelfor occultation astrometry offer the opportunity to test its global astrometricperformance on the existing data set of observed events, dominated by minorplanets belonging to the main belt.  Aims: We aim to explore the performance on orbit accuracy brought by reducingoccultations by stellar positions given in Gaia Data Release 2 (DR2) and EarlyData Release 3 (EDR3), exploited jointly with the new occultation error model.Our goal is to verify that the quality of DR2 and EDR3 provides a logicalprogression in the exploitation of occultation astrometry with respect toprevious catalogues. We also want to compare the post-fit residuals to theerror model.  Methods: We began with accurate orbit adjustment to occultation data, eitheralone or joined to the other available ground-based observations. We thenanalyzed the orbit accuracy and the post-fit residuals.  Results: Gaia EDR3 and DR2 bring a noticeable improvement to the accuracy ofoccultation data, bringing an average reduction of their residuals upon fittingan orbit of about a factor of 5 when compared to other catalogues. This isparticularly visible when occultations alone are used, resulting in very goodorbits for a large fraction of objects. We demonstrate that occultationastrometry can reach the performance of Gaia on small asteroids. The joint useof archival data and occultations remains more challenging due to the higheruncertainties and systematic errors of other data, mainly obtained bytraditional CCD imaging.

Asteroid astrometry by stellar occultations: Accuracy of the existing sample from orbital fitting