1999A&A...348..501M

New observations of AGB circumstellar envelopes made with the mid-IR imaging camera CAMIRAS are presented. Diagnostic tools based on mid-IR colors are proposed for the analysis of the observed objects, and tested against a larger sample of AGB sources derived from IRAS observations. Radiative transfer modelling is used to calibrate our diagnostic procedures, in order to investigate the physical and chemical characteristics of both samples. The different chemical signatures of C-rich and O-rich envelopes are put in evidence by mid-IR color-color diagrams, and correlations are found between the observed colors and a mass loss parameter derived by radio observations. Evidences for possible temporal variations in the mass loss rates are also suggested. The possibility to derive direct information on the spatial structure and symmetry of the envelopes is finally investigated, and the image of the O-rich star WX Psc, as an example of a spatially resolved axisymmetric envelope, is presented.