Winds from Luminous Late‐Type Stars. I. The Effects of Nonlinear Alfven Waves

Airapetian, Vladimir; Ofman, L.; Robinson, R. D.; Carpenter, K. G.; Davila, J. M.

doi:10.1086/308198

Cited by 44 publications

(60 citation statements)

References 22 publications

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“…Direct momentum input from Alvén waves seems to be a promising mechanism for driving the winds of red giants and possibly red supergiants (Airapetian et al 2000(Airapetian et al , 2010Cranmer and Saar 2011), but there is doubt if it extends to the typical stellar parameter regime of AGB stars, and especially to the cooler part of the effective temperature range, where the highest mass-loss rates are found. A lack of free charges (low degree of ionization) may prevent the gas from coupling to the magnetic field, as the photospheric UV flux decreases dramatically with a lower effective temperature of the star.…”

Section: Other Wind-driving Mechanisms In Cool Starsmentioning

confidence: 99%

“…A common assumption in wave-driven wind models for cool giant stars is direct momentum input (wave pressure), in contrast to dissipative heating and high gas pressure. While early linear models of winds driven by Alvén waves had to invoke a dissipation mechanism in order to avoid too high flow velocities (e.g., Hartmann and MacGregor 1980), more recent non-linear numerical simulations of red giant star winds do not suffer from this problem (Airapetian et al 2000(Airapetian et al , 2010. The assumptions about the thermal structure of the atmosphere in these models, however, tend to be simplistic (e.g., isothermal), and the actual wave-generation mechanisms are not part of the wind models, introducing free parameters.…”

Section: Other Wind-driving Mechanisms In Cool Starsmentioning

confidence: 99%

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Mass loss of stars on the asymptotic giant branch

Höfner

Olofsson

2018

Astron Astrophys Rev

441

376

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As low-and intermediate-mass stars reach the asymptotic giant branch (AGB), they have developed into intriguing and complex objects that are major players in the cosmic gas/dust cycle. At this stage, their appearance and evolution are strongly affected by a range of dynamical processes. Large-scale convective flows bring newlyformed chemical elements to the stellar surface and, together with pulsations, they trigger shock waves in the extended stellar atmosphere. There, massive outflows of gas and dust have their origin, which enrich the interstellar medium and, eventually, lead to a transformation of the cool luminous giants into white dwarfs. Dust grains forming in the upper atmospheric layers play a critical role in the wind acceleration process, by scattering and absorbing stellar photons and transferring their outward-directed momentum to the surrounding gas through collisions. Recent progress in high-angularresolution instrumentation, from the visual to the radio regime, is leading to valuable new insights into the complex dynamical atmospheres of AGB stars and their windforming regions. Observations are revealing asymmetries and inhomogeneities in the photospheric and dust-forming layers which vary on time-scales of months, as well as more long-lived large-scale structures in the circumstellar envelopes. High-angularresolution observations indicate at what distances from the stars dust condensation occurs, and they give information on the chemical composition and sizes of dust grains in the close vicinity of cool giants. These are essential constraints for building B Susanne Höfner

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Section: Other Wind-driving Mechanisms In Cool Starsmentioning

confidence: 99%

Section: Other Wind-driving Mechanisms In Cool Starsmentioning

confidence: 99%

Mass loss of stars on the asymptotic giant branch

Höfner

Olofsson

2018

Astron Astrophys Rev

441

376

View full text Add to dashboard Cite

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“…However, the same process is expected to operate in other types of stars that have surface convective layer, such as red giant stars, proto-stars, and intermediate and low mass main sequence stars. Red giant winds are studied in 1-D steadystate calculations (Hartmann and MacGregor , 1980) and 2-D dynamical simulations (Airapetian et al, 2000), although these studies do not set photosphere as the inner boundaries but arbitrary higher altitudes. We simulation red giant winds from the photosphere by extending the solar wind simulation (Suzuki, 2007).…”

Section: Application To Red Giant Windsmentioning

confidence: 99%

Coronal heating and wind acceleration by nonlinear Alfvén waves – global simulations with gravity, radiation, and conduction

Suzuki

2008

Nonlin. Processes Geophys.

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Abstract. We review our recent results of global onedimensional (1-D) MHD simulations for the acceleration of solar and stellar winds. We impose transverse photospheric motions corresponding to the granulations, which generate outgoing Alfvén waves. We treat the propagation and dissipation of the Alfvén waves and consequent heating from the photosphere by dynamical simulations in a self-consistent manner. Nonlinear dissipation of Alfven waves becomes quite effective owing to the stratification of the atmosphere (the outward decrease of the density). We show that the coronal heating and the solar wind acceleration in the open magnetic field regions are natural consequence of the footpoint fluctuations of the magnetic fields at the surface (photosphere). We find that the properties of the solar wind sensitively depend on the fluctuation amplitudes at the solar surface because of the nonlinearity of the Alfvén waves, and that the wind speed at 1 AU is mainly controlled by the field strength and geometry of flux tubes. Based on these results, we point out that both fast and slow solar winds can be explained by the dissipation of nonlinear Alfvén waves in a unified manner. We also discuss winds from red giant stars driven by Alfvén waves, focusing on different aspects from the solar wind.

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“…Examples of large chromospheric extent include M-type supergiants (Hartmann & Avrett 1984;Airapetian et al 2000). Considering the upper chromosphere as a starting point of the stellar wind, the implication is that a relatively low amount of potential energy is required to initiate the wind, if it starts further away from the photosphere.…”

Section: Introductionmentioning

confidence: 99%

A critical test of empirical mass loss formulas applied to individual giants and supergiants

Schröder

Cuntz

2007

A&A

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To test our new, improved Reimers-type mass-loss relation, given by Schröder & Cuntz in 2005 (ApJ, 630, L73), we take a look at the best studied galactic giants and supergiants -particularly those with spatially resolved circumstellar shells and winds, obtained directly or by means of a companion acting as a probing light source. Together with well-known physical parameters, the selected stars provide the most powerful and critical observational venues for assessing the validity of parameterized mass-loss relations for cool winds not driven by molecules or dust. In this study, star by star, we compare our previously published relation with the original Reimers relation (1975, Mem. Roy. Soc. Liège 6. Ser. 8, 369), the Lamers relation (1981, ApJ, 245, 593), and the two relations by de Jager and his group (1988, A&AS, 72, 259; 1990, A&A, 231, 134). The input data, especially the stellar masses, have been constrained using detailed stellar evolution models. We find that only the relationship by Schröder & Cuntz agrees, within the error bars, with the observed mass-loss rates for all giants and supergiants.

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Winds from Luminous Late‐Type Stars. I. The Effects of Nonlinear Alfven Waves

Cited by 44 publications

References 22 publications

Mass loss of stars on the asymptotic giant branch

Mass loss of stars on the asymptotic giant branch

Coronal heating and wind acceleration by nonlinear Alfvén waves – global simulations with gravity, radiation, and conduction

A critical test of empirical mass loss formulas applied to individual giants and supergiants

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