Abstract. In this paper, we present mean gas and dust opacities relevant to the physical conditions typical of protoplanetary discs. As the principal absorber for temperatures below ∼1500 K, we consider spherical and aggregate dust particles of various sizes, chemical structure, and porosity, consisting of ice, organics, troilite, silicates, and iron. For higher temperatures, ions, atoms, molecules, and electrons are included as the main opacity sources. Rosseland and Planck mean opacities are calculated for temperatures between 5 K and 10 000 K and gas densities ranging from 10 −18 g cm −3 to 10 −7 g cm −3 . The dependence on the adopted model of dust grains is investigated. We compare our results with recent opacity tables and show how different opacity models affect the calculated hydrodynamical structure of accretion discs.

Circumstellar dust, the astronomical dust that forms around a star, provides today's researchers with important clues for understanding how the Universe has evolved. This volume examines the structure, dynamics and observable consequences of the dust clouds surrounding highly evolved stars on the Giant Branch. Early chapters cover the physical and chemical basis of the formation of dust shells, the outflow of matter, and condensation processes, while offering detailed descriptions of techniques for calculating dust formation and growth. Later chapters showcase a wide range of modeling strategies, including chemical and radiative transfer and dust-induced non-linear dynamics, as well as the latest data obtained from AGB stars and other giants. This volume introduces graduate students and researchers to the theoretical description for modeling the dusty outflows from cool stars and provides a full understanding of the processes involved.

Abstract.We derive an improved description of dust-driven stellar mass-loss for the cool winds of carbon-rich tip-AGB stars. We use pulsating wind models in which the mass loss is driven by radiation pressure on dust grains, for C-rich chemistry. From a larger set of these models, selected for representative dynamical (pulsational velocity amplitude ∆v, period P ) and chemical (the C/ O abundance ratio) input parameters, an improved approximative mass-loss formula has been derived which depends only on the stellar parameters (effective temperature T eff , luminosity L and mass M ). Due to the detailed consideration of the chemistry and the physics of the dust nucleation and growth processes, there is a particularly strong dependence of the mass-loss rateṀ (in M /yr) onThe dependence of the model mass-loss on the pulsational period has explicitly been accounted for in connection with the luminosity dependence, by applying an observed period-luminosity relation for C-rich Miras. We also apply the improved mass-loss description to our evolution models, and we revisit their tip-AGB mass-loss histories and the total masses lost, in comparison to our earlier work with a preliminary mass-loss description. While there is virtually no difference for the models in the lower mass range of consideration (Mi = 1.0 to ≈ 1.3 M ), we now find more realistic, larger superwind mass-loss rates for larger stellar masses: i.e.,Ṁ between ≈0.4 and 1.0 × 10 −4 M /yr for Mi between 1.85 and 2.65 M , removing between 0.6 and 1.2 M , respectively, during the final 30 000 yrs on the tip-AGB.

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Abstract.We present a self-consistent time-dependent model for the oxygen-rich Mira variable IRC -20197. This model includes a consistent treatment of the interactions among hydrodynamics, thermodynamics, radiative transfer, equilibrium chemistry, and heterogeneous dust formation with TiO 2 nuclei. The model is determined by the stellar parameters, stellar mass4 L , stellar temperature T = 2400 K, and solar abundances of the elements. The pulsation of the star is simulated by a piston at the inner boundary where the velocity varies sinusoidally with a period of P = 636 d and an amplitude of ∆v p = 8 km s −1 . Based on the atmospheric structure resulting from this hydrodynamic calculation at different phases, we have performed angle-and frequency-dependent continuum radiation transfer calculations, which result in the spectral energy distributions at different phases of the pulsation cycle and in synthetic light curves at different wavelengths. These are in good agreement with the infrared observations of IRC -20197. The model yields a time averaged outflow velocity of 11.9 km s −1 and an average mass loss rate of 7.3 × 10 −6 M yr −1 which are in good agreement with the values derived from radio observations. Furthermore, the chemical composition of the resulting grains is discussed.