2000A&A...354..657L

Radiative transfer modelling of the dust envelope of the post-AGB (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 µm in radius are required in the model to fit the observations. We estimate the mass of the dust envelope to be about 4.4x10^–2M_☉ assuming a distance of 1000pc. 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 7.0M_☉. We compare our results to those of a recently published paper (Skinner et al. 1997A&A...328..290S) and compare our model geometry to a sketch proposed by Sahai et al. (1998ApJ...493..301S).