A dust envelope modelling of the Egg Nebula

Radiative transfer modelling of the dust envelope of the post-AGE (post-Asymptotic Giant Branch) object called the Egg nebula is proposed in non-spherical geometry. The present work follows a previous study by Yusef-Zadeh et al. (1984) in which the dust density law smoothly decreases with latitude above and below the midplane of a disk shaped envelope. The model we present reproduces the broad band spectrum and the bipolar structures of the Egg nebula as observed at various wavelengths from visible to mid-infrared. Dust particles as large as 8 mu m in radius are required in the model to fit the observations. We estimate the mass of the dust envelope to be about 4.4 x 10(-2)M(circle dot) assuming a distance of 1000 pc. According to a mass ratio of gas to dust of 158 (Knapp 1986), the total mass of the envelope of the Egg Nebula is estimated to be 7.0 Mo. We compare our results to those of a recently published paper (Skinner et al. 1997) and compare our model geometry to a sketch proposed by Sahai et al. (1998b).