Self-consistent coupling of radiative transfer and dynamics in dust-driven winds

Liberatore, S.; Lafon, J. P. J.; Berruyer, N.

doi:10.1051/0004-6361:20011115

Cited by 10 publications

(9 citation statements)

References 36 publications

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“…After decades of theoretical and observational studies, the mechanisms in which the wind acceleration occurs are still poorly understood. Due to the stellar high luminosity and low effective temperature, several authors have proposed radiativelly dust‐driven models to explain the observed wind properties (Elitzur & Ivezic 2001; Liberatore, Lafon & Berruyer 2001; Woitke & Niccolini 2005). At the pulsating phase, acoustic waves generate high‐density shells that could allow dust to form near the stellar surface.…”

Section: Introductionmentioning

confidence: 99%

On the magnetic structure and wind parameter profiles of Alfvén wave driven winds in late-type supergiant stars

Falceta‐Gonçalves¹,

Vidotto²,

Jatenco‐Pereira³

2006

Monthly Notices of the Royal Astronomical Society

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Cool stars at giant and supergiant evolutionary phases present low-velocity and high-density winds, responsible for the observed high mass-loss rates. Although presenting high luminosities, radiation pressure on dust particles is not sufficient to explain the wind acceleration process. Among the possible solutions to this still unsolved problem, Alfvén waves are, probably, the most interesting for their high efficiency in transfering energy and momentum to the wind. Typically, models of Alfvén wave driven winds result in high-velocity winds if they are not highly damped. In this work, we determine self-consistently the magnetic field geometry and solve the momentum, energy and mass conservation equations, to demonstrate that even a low-damped Alfvén wave flux is able to reproduce the low-velocity wind. We show that the magnetic flux tubes expand with a super-radial factor of S > 30 near the stellar surface, larger than that used in previous semi-empirical models. The rapid expansion results in a strong spatial dilution of the wave flux. We obtained the wind parameter profiles for a typical supergiant star of 16 M . The wind is accelerated in a narrow region, coincident with the region of high divergence of the magnetic field lines, up to 100 km s −1 . For the temperature, we obtained a slight decrease near the surface for low-damped waves, because the wave heating mechanism is less effective than the radiative losses. The peak temperature occurs at r 1.5 r 0 reaching 6000 K. Propagating outwards, the wind cools down mainly due to adiabatic expansion.

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Section: Introductionmentioning

confidence: 99%

On the magnetic structure and wind parameter profiles of Alfvén wave driven winds in late-type supergiant stars

Falceta‐Gonçalves¹,

Vidotto²,

Jatenco‐Pereira³

2006

Monthly Notices of the Royal Astronomical Society

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“…So far this phenomenon has almost exclusively been studied in stationary winds (e.g. Krüger et al 1994, henceforth KGS94;Krüger & Sedlmayr 1997;or Liberatore et al 2001) or non-pulsating stars (e.g. Simis et al 2001;or Sandin & Höfner 2003, henceforth Paper I).…”

Section: Introductionmentioning

confidence: 99%

Three-component modeling of C-rich AGB star winds

Sandín

Höfner

2003

A&A

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Abstract. We present three-component wind models for carbon-rich pulsating AGB stars. In particular we study the effects of drift in models of long-period variables, meaning that the dust is allowed to move relative to the gas (drift models). In addition we investigate the importance of the degree of variability of the wind structures. The wind model contains separate conservation laws for each of the three components of gas, dust and the radiation field. We use two different representations for the gas opacity, resulting in models with different gas densities in the wind. The effects which we investigate here are important for the understanding of the wind mechanism and mass loss of AGB stars. This study is hereby a necessary step towards more reliable interpretations of observations. We find that the effects of drift generally are significant. They cannot be predicted from models calculated without drift. Moreover, the non-drift models showing the lowest mass loss rates, outflow velocities, and the smallest variability in the degree of condensation do not form drift model winds. The wind formation in drift models is, except for a few cases, generally less efficient and the mass loss consequently lower than in the corresponding non-drift models. The effects of drift are generally larger in the more realistic models using that representation of the gas opacity which results in lower densities. The outflow properties of these models are also -for all cases we have studied -sensitive to the period of the stellar pulsations. A check of the mass loss rates against a (recent) fit formula shows systematically lower values, in particular in the more realistic models with a low density. The fit is in its current form inapplicable to the new models presented here.

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“…We have added the diffusive collisions term to the first two approximations. Berruyer & Frisch derived the following approximation of C D,common (see also, Liberatore et al 2001;Mastrodemos et al 1996),…”

Section: Numerical Issues In the Rhd3-systemmentioning

confidence: 99%

“…However, without detailed modeling it is not clear quantitatively how large the effect due to the coupling will be. The most recent works concerning the influence of the treatment of the gas and dust phases have been carried out by Liberatore et al (2001), SID01 and Steffen et al (1998). An overview of the handling of the gas-dust interaction in earlier AGB wind models is presented by SID01.…”

Section: Introductionmentioning

confidence: 99%

Three-component modeling of C-rich AGB star winds

Sandín

Höfner

2003

A&A

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Abstract. Radiative acceleration of newly-formed dust grains and transfer of momentum from the dust to the gas plays an important role for driving winds of AGB stars. Therefore a detailed description of the interaction of gas and dust is a prerequisite for realistic models of such winds. In this paper we present the method and first results of a three-component time-dependent model of dust-driven AGB star winds. With the model we plan to study the role and effects of the gas-dust interaction on the mass loss and wind formation. The wind model includes separate conservation laws for each of the three components of gas, dust and the radiation field and is developed from an existing model which assumes position coupling between the gas and the dust. As a new feature we introduce a separate equation of motion for the dust component in order to fully separate the dust phase from the gas phase. The transfer of mass, energy and momentum between the phases is treated by interaction terms. We also carry out a detailed study of the physical form and influence of the momentum transfer term (the drag force) and three approximations to it. In the present study we are interested mainly in the effect of the new treatment of the dust velocity on dust-induced instabilities in the wind. As we want to study the consequences of the additional freedom of the dust velocity on the model we calculate winds both with and without the separate dust equation of motion. The wind models are calculated for several sets of stellar parameters. We find that there is a higher threshold in the carbon/oxygen abundance ratio at which winds form in the new model. The winds of the new models, which include drift, differ from the previously stationary winds, and the winds with the lowest mass loss rates no longer form.

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Self-consistent coupling of radiative transfer and dynamics in dust-driven winds

Cited by 10 publications

References 36 publications

On the magnetic structure and wind parameter profiles of Alfvén wave driven winds in late-type supergiant stars

On the magnetic structure and wind parameter profiles of Alfvén wave driven winds in late-type supergiant stars

Three-component modeling of C-rich AGB star winds

Three-component modeling of C-rich AGB star winds

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