THE DUST JETS OF P-SWIFT-TUTTLE 1992T

Comet P/Swift-Tuttle 1992t was observed during 17 nights from 20 November to 21 December 1992 at the Pic du Midi Observatory. The CCD images obtained by the 1.05 m telescope showed the existence of spiral dust jets. In particular, a strong dust jet was easily detectable on the high resolution images in late November. We used a preliminary simple model, in which we neglected the solar radiation pressure, to derive the rotation period (2.7-2.9 days) and the spin axis orientation of the nucleus. We also determined an expansion velocity of the dust of 0.3 km s-1 in the jet and an opening angle of 20-degrees. The comparison with the 1862 passage of P/Swift-Tuttle seems to indicate that the rotation period is constant, but that the spin axis could precess.