1995A&A...302..483W

Theoretical brightness profiles and spatial spectra of dynamical models for circumstellar dust shells of long-period variables are presented. Based on dynamical models of circumstellar dust shells, which include time-dependent hydrodynamics and a detailed treatment of the processes of formation, growth and evaporation of carbon grains, frequency-dependent radiative transfer calculations have been carried out which yield the synthetic brightness distributions and spatial spectra of these dust shell models. The brightness profiles show a pronounced time-dependent internal structure on a spatial scale of a few stellar radii, which reflects the discrete shell-like distribution of dust across the circumstellar shell. Internal structures are also present in the synthetic spatial spectra (or visibilities) calculated from these intensity profiles. Similar structures, which are present in the observed brightness profiles and spatial spectra of several long-period variable stars can be physically explained by the formation of discrete dust layers resulting from the model calculations presented here. We also find temporal variations of the synthetic spatial spectra which are in quantitative agreement with respective observations. Our model calculations indicate, that the instants of time, when the minimum and maximum value of the visibility is reached depend on wavelength.