Determination of the Mass of (1) Ceres from Perturbations on (203) Pompeja and (348) May

We collected 223 observations of Pompeja from 1879-1990 and 88 observations of May from 1892-1991 to use them for improvement of orbits of the asteroids and for determination of the mass of Ceres. We applied the recurrent power series method to integrate numerically equations of motion of Pompeja and of May as disturbed by Ceres; in the observational interval both asteroids approached Ceres closer than to 0.1 a.u. twice. We created thirteen normal equations, corresponding to 589 observational equations, to correct by the least squares method the mass of Ceres along with orbital elements of Pompeja and of May. We found the mass of Ceres equal to (4.796 pm 0.085) times 10^{-10} in solar unit mass.