Dynamic atmosphere and wind models of C-type asymptotic giant branch stars. Influences of dust optical data on mass loss and observables

Abstract

Mass loss through stellar winds governs the evolution of stars on the asymptotic giant branch (AGB). In the case of carbon-rich AGB stars, the wind is believed to be driven by radiation pressure on amorphous carbon (amC) dust forming in the atmosphere. The choice of dust optical data will have a significant impact on atmosphere and wind models of AGB stars. We compare two commonly used optical data sets of amC and investigate how the wind characteristics and photometric properties resulting from dynamical models of carbon-rich AGB stars are influenced by the micro-physical properties of dust grains. We computed two extensive grids of carbon star atmosphere and wind models with the DARWIN 1D radiation-hydrodynamical code. Each of the two grids uses a different amC optical data set. The stellar parameters of the models were varied to cover a wide range of possible combinations. A posteriori radiative transfer calculations were performed for a sub-set of the models, resulting in photometric fluxes and colours. We find small, but systematic differences in the predicted mass-loss rates for the two grids. The grain sizes and photometric properties are affected by the different dust optical data sets. Higher absorption efficiency leads to the formation of a greater number of grains, which are smaller. Models that are obscured by dust exhibit differences in terms of the covered colour range compared to observations, depending on the dust optical data used. An important motivation for this study was to investigate how strongly the predicted mass-loss rates depend on the choice of dust optical data, as these mass-loss values are more frequently used in stellar evolution models. Based on the current results, we conclude that mass-loss rates may typically differ by about a factor of two for DARWIN models of C-type AGB stars for commonly used dust optical data sets.

12 pages, 9 figures. Accepted for publication in Astronomy & Astrophysics

References in corpus (11)

• Constraining the thermally-pulsing asymptotic giant branch phase with resolved stellar populations in the Small Magellanic Cloud
• Carbon star formation as seen through the non-monotonic initial-final mass relation
• Luminosities and mass-loss rates of Local Group AGB stars and Red Supergiants
• Dust-driven Winds and Mass Loss of C-rich AGB Stars with subsolar Metallicities
• Synthetic photometry for carbon-rich giants. IV. An extensive grid of dynamic atmosphere and wind models
• Constraining dust properties in Circumstellar Envelopes of C-stars in the Small Magellanic Cloud: optical constants and grain size of Carbon dust
• The mass-loss, expansion velocities and dust production rates of carbon stars in the Magellanic Clouds
• Global 3D radiation-hydrodynamical models of AGB stars with dust-driven winds
• Carbon star wind models at solar and sub-solar metallicities: a comparative study. I. Mass loss and the properties of dust-driven winds
• Carbon stars with increased oxygen and nitrogen abundances: hydrostatic dust-free model atmospheres
• Synthetic photometry for carbon-rich giants. V. Effects of grain-size-dependent dust opacities