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A. Cellino (Torino Astronomical Observatory), E. Diolaiti (Padova Astronomical Observatory), A. Ghedina (Telescopio Nazionale Galileo), D. Hestroffer (IMC Observatoire de Paris), R. Ragazzoni (Padova Astronomical Observatory), P. Tanga (Torino Astronomical Observatory)
The Speckle camera of the 3.5 m Telescopio Nazionale Galileo (TNG) has been used to measure apparent sizes and shapes of a number of main belt asteroids. The size measurements are in a generally good agreement (within about 10%) with the results of indirect IRAS-based radiometric techniques. The measured shapes are compared with predictions based on previously derived spin axis directions and lightcurve photometry of some of the observed objects. Also in this case the agreement is reasonable, and the speckle observations may allow us to discriminate between the two pole solutions usually found for each object. No clear evidence of binaries was found, although the asteroid 135 Hertha turns out to be much more elongated than previously suspected. The results show that the TNG speckle camera can be a powerful tool to resolve relatively large main belt asteroids, and to calibrate the results of the IRAS survey. Direct shape measurements may also permit to obtain some estimate of the densities of the objects, when the rotational period is known and assuming they have equilibrium shapes, or when mass estimates are independently available.