Abstract. We present submillimeter observations of rotational transitions of carbon monoxide from J = 2 → 1 up to 7 → 6 for a sample of Asymptotic Giant Branch stars and red supergiants. It is the first time that the high transitions J = 6 → 5 and 7 → 6 are included in such a study. With line radiative transfer calculations, we aim to determine the mass-loss history of these stars by fitting the CO line intensities. We find that the observed line intensities of the high transitions, including the J = 4 → 3 transition, are significantly lower than the predicted values. We conclude that the physical structure of the outflow of Asymptotic Giant Branch stars is more complex than previously thought. In order to understand the observed line intensities and profiles, a physical structure with a variable mass-loss rate and/or a gradient in stochastic gas velocity is required. A case study of the AGB star WX Psc is performed. We find that the CO line strengths may be explained by variations in mass-loss on time scales similar to those observed in the separated arc-like structures observed around post-AGB stars. In addition, a gradient in the stochastic velocity may play a role. Until this has been sorted out fully, any mass loss determinations based upon single CO lines will remain suspect.

We present the classification of 197 point sources observed with the Infrared Spectrograph in the SAGE-Spec Legacy programme on the Spitzer Space Telescope. We introduce a decisiontree method of object classification based on infrared spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership and variability information, which is used to classify the SAGE-Spec sample of point sources. The decision tree has a broad application to mid-infrared spectroscopic surveys, where supporting photometry and variability information are available. We use these classifications to make deductions about the stellar populations of the Large Magellanic Cloud and the success of photometric classification methods. We find 90 asymptotic giant branch (AGB) stars, 29 young stellar objects, 23 post-AGB objects, 19 red supergiants, eight stellar photospheres, seven background galaxies, seven planetary nebulae, two H II regions and 12 other objects, seven of which remain unclassified.

We present 7-14 mm Infrared Space Observatory (ISO) spectroscopy of 12 M-type evolved stars in the Large Magellanic Cloud (LMC), in order to study the dust mineralogy and condensation process around these stars. The sample stars show a broad dust feature in the 7-14 mm region, which is seen in either emission or (self-) absorption. The shape of the feature changes with increasing mass-loss rate, , suggesting a change in dusṫ M mineralogy as the central star evolves. At low mass-loss rates amorphous alumina and amorphous silicates are observed, while at high mass-loss rates only amorphous silicates are seen, in agreement with the classical condensation sequence expected for these materials. We find a clear correlation between and the peak wavelengtḣ M position of the broad dust feature. Our data suggest a strong dependence of the dust mineralogy on the temperature at the dust condensation radius.

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