  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 evolutionary 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.
  In this paper we analyse new sub-millimetre observations of 9 evolved stars
in order to constrain the CSE physical parameters. The data were taken by the
new APEX bolometer LABoCa.
  The fluxes at 870 um are derived and the extended emission is investigated.
  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.
  We detected the presence of extended emission around four stars. Physical
parameters of the circumstellar envelope are derived from SED modelling, such
as the dust chemical composition, the dust condensation temperature and the
total mass of the envelope. It proves difficult however to fit the SED and the
intensity profile simultaneously.
