The hydrodynamical structure of circumstellar envelopes around low mass-loss rate, low outflow velocity AGB stars^*

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² DEMIRM, UMR 8540, Observatoire de Paris, 61 av. de l'Observatoire, 75014 Paris, France
³ Swedish-ESO Submillimetre Telescope, European Southern Observatory, Casilla 19001, Santiago 19, Chile
⁴ Institut d'Astrophysique de Paris, CNRS, 98bis Boulevard Arago, 75014 Paris, France

Corresponding author: J. M. Winters, jwinters@mpifr-bonn.mpg.de

Received: 23 November 2001
Accepted: 3 April 2002

Abstract

Recent hydrodynamical models (Winters et al. 2000b) allow the existence of pulsating, large velocity amplitude Asymptotic Giant Branch (AGB) stars with tenuous dusty circumstellar shells, which produce low mass-loss rates and simultaneously low wind velocities. The Semi-regular long-period variable L² Pup shows a broad SiO maser feature at 86 GHz (, ), indicating an outward velocity of the material close to the stellar photosphere of at least 10 km s^-1 , and narrow CO () and (1-0) line profiles indicating an outflow velocity of the material in the circumstellar shell of only about 3 km s^-1 . This can be explained in terms of our hydrodynamical models which provide large velocities in the shocked stellar atmosphere and low velocities of the circumstellar outflow.