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Astron. Astrophys. 354, 657-666 (2000)


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A dust envelope modelling of the Egg Nebula

B. Lopez 1 and J.-M. Perrin 2

1 Observatoire de la Côte d'Azur, Département Fresnel UMR 6528, B.P. 4229, 06034 Nice Cedex 4, France
2 Observatoire de Haute Provence, UPR A9049, 04870 Saint Michel l'Observatoire, France

Received 7 July 1999 / Accepted 29 September 1999

Abstract

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 [FORMULA] in radius are required in the model to fit the observations. We estimate the mass of the dust envelope to be about [FORMULA][FORMULA] 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 [FORMULA]. 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).

Key words: radiative transfer – stars: circumstellar matter – stars: AGB and post-AGB – ISM: individual objects:

Send offprint requests to: Bruno Lopez (lopez@obs-nice.fr)

© European Southern Observatory (ESO) 2000

Online publication: February 9, 2000

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