Earth-bound observations of asteroid 19 Fortuna as support to HST imaging: lightcurves, pole direction and shape

To support the 19 Fortuna imaging work performed by the Hubble Space Telescope, this asteroid was photoelectrically observed in September 1993 at Mt. John, Lake Tekapo and Serra la Nave observatories, covering a complete rotational cycle. These observations and the unpublished ones, collected in November 1986 at Torino Observatory, allowed us to compute the value of the synodic rotational period, which results in accordance with that already known. The spin axis direction and the shape of 19 Fortuna were determined by applying the amplitude-magnitude method (Zappalà et al., in Asteroids, Comets, Meteors (edited by C.-I. Lagerkvist and H. Rickman), pp. 73–76. Uppsala Univeritet, Reprocentralen, HSC, Uppsala, 1983) to our data and to those reported in the literature. The values of the pole coordinates are in agreement with the previous determinations, while the ratio between the semi-axes a and b is larger than about 0.1.