Parameters for the dust envelope of the protoplanetary nebula IRAS 18062+2410

We have calculated a model for the dust envelope of the protoplanetary nebu la IRAS 18062 + 2410 using observations from the ultraviolet to the far inf rared. We assume that the envelope is spherically symmetrical and consists of identical silicate grains with a radius of 0.10 micron, and with the num ber density of the grains inversely proportional to the square of the dista nce. The optical depth of the envelope, whose inner boundary is 1.40 x 10(- 3) pc from the center of the star, is 0.050 at 10 microns. At the inner env elope boundary, the temperature of the dust grains is 410 K and their densi ty is 2.7 x 10(-7) cm(-3). Using calculations of stellar evolution at the s tage following the exit from the asymptotic giant branch, we estimate the d ust envelope's expansion velocity to be 12 km/s. The mass-loss rate of the star preceding the ejection of the envelope was about 4.5 x 10(-6) M./yr. T he observed excess of far-IR flux is not associated with the continuum radi ation of the nebula, and may provide evidence for the presence of dust ejec ted by the star in earlier stages of its evolution. (C) 2000 MAIK "Nauka/In terperiodica".