Abstract
Recent observations of circumstellar shells at arc second resolutions (i.e., 100 R•, in the case of IRC+10216) reveal clumpy structures, asymmetries and jets. The most recent maps of such objects, observed with the IRAM Plateau de Bure interferometer and Pico Veleta telescope, are presented.
Introduction
The dusty envelopes of late type stars are fascinating objects on their own; they are also interesting for what they teach us about IS chemistry. From their velocity field and density profile, we can study the mass loss during a crucial phase of stellar evolution: since the gas expands at nearly constant velocity in all, but the innermost envelope, the velocity maps yield a 3-D view of the molecule spatial distribution; the distributions of the different molecular species show how photochemical, molecule-molecule and grainsurface reactions proceed with time in a well behaved environment.
The closest massive envelopes lie a few hundred parsecs away and have small angular sizes. The construction of large millimeter-wave interferometers, in particular the IRAM Plateau de Bure interferometer (Guilloteau et al. 1992), has provided a major breakthrough in their investigation.
Molecular emission in IRC+10216
The most remarkable and probably closest massive envelope surrounds the bright IR object IRC+10216 (CW Leo). Its outer radius, observed in the mm lines of 12CO, the most abundant molecule and the best shielded from photodissociation after H2, is R = 3′ (Guélin & Cernicharo, in preparation).