Issue |
A&A
Volume 673, May 2023
|
|
---|---|---|
Article Number | A21 | |
Number of page(s) | 13 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361/202245206 | |
Published online | 27 April 2023 |
Synthetic photometry for carbon-rich giants
V. Effects of grain-size-dependent dust opacities★
1
Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University,
Box 516,
75120
Uppsala,
Sweden
e-mail: kjell.eriksson@physics.uu.se
2
Department of Astrophysics, University of Vienna,
Türkenschanzstrasse 17,
1180
Vienna,
Austria
Received:
11
October
2022
Accepted:
25
February
2023
Context. The properties and the evolution of asymptotic giant branch (AGB) stars are strongly influenced by their mass loss through a stellar wind. This, in turn, is believed to be caused by radiation pressure due to the absorption and scattering of the stellar radiation by the dust grains formed in the atmosphere. The optical properties of dust are often estimated using the small particle limit (SPL) approximation, and it has been used frequently in modelling AGB stellar winds when performing radiation-hydrodynamics (RHD) simulations.
Aims. We aim to investigate the effects of replacing the SPL approximation by detailed Mie calculations of the size-dependent opacities for grains of amorphous carbon forming in C-rich AGB star atmospheres.
Methods. We performed RHD simulations for a large grid of carbon star atmosphere+wind models with different effective temperatures, luminosities, stellar masses, carbon excesses, and pulsation properties. Also, a posteriori radiative transfer calculations for many radial structures (snapshots) of these models were done, resulting in spectra and filter magnitudes.
Results. We find that, when giving up the SPL approximation, the wind models become more strongly variable and more dominated by gusts, although the average mass-loss rates and outflow speeds do not change significantly; the increased radiative pressure on the dust throughout its formation zone does, however, result in smaller grains and lower condensation fractions (and thus higher gas-to-dust ratios). The photometric K magnitudes are generally brighter, but at V the effects of using size-dependent dust opacities are more complex: brighter for low mass-loss rates and dimmer for massive stellar winds.
Conclusions. Given the large effects on spectra and photometric properties, it is necessary to use the detailed dust optical data instead of the simple SPL approximation in stellar atmosphere+wind modelling where dust is formed.
Key words: stars: AGB and post-AGB / stars: carbon / stars: winds, outflows
Full Table C.1 is only available at the CDS via anonymous ftp to cdsarc.cds.unistra.fr (130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/673/A21
© The Authors 2023
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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