870µm observations of evolved stars with LABOCA.?

Context. During their evolution, Asymptotic Giant Branch (AGB) stars experience a high mass-loss which leads to the formation of a Circumstellar Envelope (CSE) of dust and gas. The mass-loss process is the most important phenomenon during this evolution-ary stage. In order to understand it, it is important to study the physical parameters of the CSE. The emission of the CSE in the (sub)millimetre range is dominated by the dust continuum. This means that (sub)millimetre observations are a key tool in tracing the dust and improving our knowledge of the mass-loss process. Aims. The aim of this study is to use new sub-millimetre observations of a sample of evolved stars to constrain the CSE physical parameters. Methods. We used aperture photometry to determine the fluxes at 870µm and to investigate the extended emission observed using the new APEX bolometer LABoCa. We compute the spectral energy distribution (SEDs) using a 1D radiative transfer code, DUSTY which we compared to literature data. Grain properties are calculated using both spherical grains distribution and a Continuous Distribution of Ellipsoids (CDE) and a comparison between the two is drawn. Synthetic surface brightness maps have been derived from the modelling and were compared to the LABoCa brightness maps. Results. A sample of nine evolved stars with different chemistry has been observed with LABoCa. We detected the presence of extended emission around four stars. Physical parameters of the circumstellar envelope are derived from SED modelling, such as th