open access

https://hdl.handle.net/2115/66490

Dust formation and mass loss around intermediate-mass AGB stars with initial metallicity $Z_{ini} <= 10^{-4}$ in the early Universe - I. Effect of surface opacity on stellar evolution and the dust-driven wind

英語

dust, extinction

2017-04

Oxford University Press

Monthly notices of the royal astronomical society

466(2)

1709-1732

Dust formation and the resulting mass loss around asymptotic giant branch (AGB) stars with initial metallicity in the range $0 ≤ Z_{ini} ≤ 10^{-4}$ and initial mass $2 ≤ M_{ini}/M_⦿ ≤ 5$ are explored by hydrodynamical calculations of the dust-driven wind (DDW) along the AGB evolutionary tracks. We employ the MESA code to simulate the evolution of stars, assuming an empirical mass-loss rate in the post-main-sequence phase and considering three types of low-temperature opacity (scaled-solar, CO-enhanced and CNO-enhanced opacity) to elucidate the effect on stellar evolution and the DDW. We find that the treatment of low-temperature opacity strongly affects dust formation and the resulting DDW; in the carbon-rich AGB phase, the maximum. $\dot{M}$ of $M_{ini} ≥ 3M_⦿$ stars with the CO-enhanced opacity is at least one order of magnitude smaller than that with the CNO-enhanced opacity. A wide range of stellar parameters being covered, the necessary condition for driving efficient DDW with. $\dot{M} ≥ 10^{-6} M_⦿ yr^{-1}$ is expressed as effective temperature $T_{eff} ≲ 3850 K$ and $\log(\delta_CL/\kappa_RM) ≳ 10.43 \log T_{eff} -32.33$, with the carbon excess $\delta_C$ defined as $\epsilon_C - \epsilon_O$, the Rosseland mean opacity. $\kappa_R$ in units of $cm^2 g^{-1}$ in the surface layer and the stellar mass (luminosity) $M(L)$ in solar units. The fitting formulae derived for gas and dust mass-loss rates in terms of input stellar parameters could be useful for investigating the dust yield from AGB stars in the early Universe being consistent with stellar evolution calculations.

学術雑誌論文

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This article has been accepted for publication in Monthly notices of the royal astronomical society ©2016 The Authors Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved.

0035-8711