• Barlow, Mj
• Bowey, Janet
• Ercolano, B.
• Epitácio Pereira, D. N.
• De Araújo, F. X.
• Lorenz-Martins, S.

Abstract

Post-AGB stars are among the most important sources of dust enrichment of the interstellar medium. Molster et al. (2002, A&amp;A, 382, 184) investigated the mineralogy and occurrence of crystalline silicate grain features around evolved stars, and concluded that, for the sharpest featured sources, the grains are located in a cool circumstellar envelope, rather than in the matter outflows. As the envelope is formed from the mass loss from the central star, one would expect the star surrounded by such silicate-rich material to be of oxygen-rich composition. However, crystalline silicates are frequently associated with carbon-rich central objects. These dual chemistry objects present an opportunity to investigate the mechanisms of mass ejection that forms the circumstellar envelope and contribute to the enrichment of the interstellar medium. In this work we present the results of a 3D Monte Carlo simulation of the radiative transfer on the circumstellar envelope of the dual chemistry post-AGB star Roberts 22. A density distribution for the dust grains surrounding the star is obtained by comparing the simulated images generated with the Monte Carlo code with those obtained and analyzed by Sahai et al. (1999, AJ, 117, 1408) with the Hubble Space Telescope. Three different species of grains were considered: amorphous carbon, amorphous silicate, crystalline silicate. The fact that many types of grains found around AGB and post-AGB stars have been found in meteorites as well, suggests a link between these stars and pre-solar grains. The morphology of the dust envelope of post-AGB stars is a key tool for the investigation of the dynamics of dust ejection of these objects, and its study can throw a new light on the origin of primitive grains. <P />...

Topics

• density
• impedance spectroscopy
• amorphous
• Carbon
• grain
• simulation
• Oxygen