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By using self-consistent dynamic model atmospheres which simulatepulsation-enhanced dust-driven winds of AGB stars we studied in detail theinfluence of (i) pulsations of the stellar interiors, and (ii) the developmentof dusty stellar winds on the spectral appearance of long period variables withcarbon-rich atmospheric chemistry. While the pulsations lead to large-amplitudephotometric variability, the dusty envelopes cause pronounced circumstellarreddening. Based on one selected dynamical model which is representative ofC-type Mira variables with intermediate mass loss rates, we calculatedsynthetic spectra and photometry for standard broad-band filters from thevisual to the near-infrared. Our modelling allows to investigate in detail thesubstantial effect of circumstellar dust on the resultant photometry. Thepronounced absorption of amorphous carbon dust grains leads to colour indiceswhich are significantly redder than the corresponding ones based on hydrostaticdust-free models. Only if we account for this circumstellar reddening we getsynthetic colours that are comparable to observations of evolved AGB stars. Thephotometric variations of the dynamical model were compared to observedlightcurves of the C-type Mira RU_Vir which appears to be quite similar to themodel. We found good agreement concerning the principal behaviour of theBVRIJHKL lightcurves and also quantitatively fitting details. The analysedmodel is able to reproduce the variations of RU_Vir and other Miras in (J-H)vs. (H-K) diagrams throughout the light cycle. Contrasting the model photometrywith observational data for a variety of galactic C-rich giants in suchcolour-colour diagrams proved that the chosen atmospheric model fits well intoa sequence of objects with increasing mass loss rates, i.e., redder colourindices.

Synthetic photometry for carbon-rich giants II. The effects of pulsation and circumstellar dust