Radiative Transfer Modeling of Periodic Mass-Loss Enhancement During the AGB Phase

Abstract

Thermally pulsing asymptotic giant branch (AGB) stars suffer mass loss which leads to the formation of a circumstellar shell of gas and dust. At the end of the AGB phase, mass-loss stops and the circumstellar shell begins to drift away from the star. Assuming the velocity of the AGB wind has been relatively constant, the history of mass loss during the AGB phase is imprinted on the dust shell of the post-AGB envelope. By studying the distribution of matter in these circumstellar shells we can gain a better understanding of the mass-loss processes involved in the evolution of these stars. Using far-infrared (IR) ISOPHOT images of the circumstellar shells of the Egg nebula and AFGL 618, we showed that dust shells can be imaged out to a radius of 2-3 pc, and that these dust shells show evidence for episodic enhancements in the mass loss with a period of ~104 years. Here, we present radiative transfer (RT) models of the dust shell around the Egg nebula using the 1-d RT code DUSTY which has been modified to include heating by the ISRFKeywordsThermal pulsesmass lossEgg nebuladust