Testing cometary ejection models to fit the 1999 Leonids and to predict future showers

Brown & Jones have discussed four models for the ejection velocities of com etary material during the perihelion passage of a comet. The ejection veloc ities depend on the heliocentric distance, density and mass of the ejected particle and on the size of the comet. For the density of the particles, th ey assumed three values, 100, 800 and 4000 kg m(-3), which give a possible combination of 12 cometary ejection models. This paper tests whether these models can be applied to explain the Leonid phenomenon for which Comet 55P/ Tempel-Tuttle is responsible. The ejection is simulated of 61 000 particles during each of the last four apparitions of Tempel-Tuttle, and flux rates on Earth are derived. The results prove that the models with a particle den sity of 4000 kg m(-3) provide the best fit to the observed Leonid rates in 1999. Based on the ejection velocity model that gives the smallest root-mea n-square error for the year 1999, noticeable displays of the Leonids are pr edicted for 2000 and 2001 November.