AGB circumstellar envelopes: molecular observations

Imaging the circumstellar envelopes of AGB stars ⋆

Aims. We report the results of an exploratory program to image the extended circumstellar envelopes of asymptotic giant branch (AGB) stars in dust-scattered galactic light. The goal is to characterize the morphology of the envelopes as a probe of the mass-loss process. Methods. The observations consist of short exposures with the VLT and longer exposures with 1–2 m telescopes, augmented with ar...

VLA Observations of H i in the Circumstellar Envelopes of AGB Stars

We have used the Very Large Array (VLA) to search for neutral atomic hydrogen (H i) in the circumstellar envelopes of five asymptotic giant branch (AGB) stars. We have detected H i 21-cm emission coincident in both position and velocity with the S-type semi-regular variable star RS Cnc. The emission comprises a compact, slightly elongated feature centered on the star with a mean diameter of ∼ 8...

The abundance of SiS in circumstellar envelopes around AGB stars

Aims. Given their photospheric origin and refractive nature, SiS molecules can provide important constraints on the relative roles of dust condensation and non-equilibrium processes in regulating the chemistry in circumstellar envelopes around evolved stars. Methods. New SiS multi-transition (sub-)millimetre line observations of a sample of AGB stars with varying photospheric C/Oratios and mass...

Molecular abundances in carbon-rich circumstellar envelopes

A millimetre molecular line survey of seven high mass-loss rate carbon stars in both the northern and southern skies is presented. A total of 196 emission lines (47 transitions) from 24 molecular species were detected. The observed CO emission is used to determine mass-loss rates and the physical structure of the circumstellar envelope, such as the density and temperature structure, using a det...

Molecular Synthesis in the External Envelopes of AGB