Title: Mid-IR Imaging of AGB Circumstellar Envelopes
Abstract: AGB stars, the precursors of Planetary Nebulae, exhibit high rates of mass loss and eject material in the form of a slow (10-20 km/s), dusty molecular wind. The general belief that the dust component of AGB circumstellar envelopes have smooth density profiles and spherical symmetry have recently been shaken by new high resolution images, showing that clumpy and asymmetric structures, analogous to the ones observed in Planetary Nebulae, can be present even before the end of the AGB. To illustrate how and when these structures appear, and possibly to address the question of how they may shape the subsequent evolution of these systems, we have started a campaign of mid-IR high spatial resolution imaging of a selected sample of AGB targets. We want here to illustrate our technique, developed for the mid-IR camera MIRAC3, and to show the first results obtained at the NASA Infrared Telescope Facility. 1. Looking for asymmetrical progenitors of PN Intermediate and low mass stars (1–8 M⊙) are characterized, in the phase known as Asymptotic Giant Branch (AGB), by the formation of an optically opacque circumstellar envelope of gas and dust, which will later evolve into a Planetary Nebula. The detailed physical processes involved in this phenomena are still uncertain, but there are growing evidences that they are connected to radial stellar oscillations and non uniform density distributions (Lebertre & Winters 1998; Fleisher et al. 1992). Recent observations at different wavelengths support the idea that these inhomogeneities can propagate in the circumstellar envelope, giving rise to structures with strong deviations from spherical symmetry. Clumpy structures in the
Publication Year: 2000
Publication Date: 2000-01-01
Language: en
Type: article
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