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G.R. Keller V. Jatenco-Pereira 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The Wolf–Rayet (WR) stars are hot luminous objects which are suffering an extreme mass loss via a continuous stellar wind. The high values of mass loss rates and high terminal velocities of the WR stellar winds constitute a challenge to the theories of radiation driven winds. Several authors incorporated magnetic forces to the line driven mechanism in order to explain these characteristics of the wind. Observations indicate that the WR stellar winds may reach, at the photosphere, velocities of the order of the terminal values, which means that an important part of the wind acceleration occurs at the optically thick region. The aim of this study is to analyze a model in which the wind in a WR star begins to be accelerated in the optically thick part of the wind. We used as initial conditions stellar parameters taken from the literature and solved the energy, mass and momentum equations. We demonstrate that the acceleration only by radiative forces is prevented by the general behavior of the opacities. Combining radiative forces plus a flux of Alfvén waves, we found in the simulations a fast drop in the wind density profile which strongly reduces the extension of the optically thick region and the wind becomes optically thin too close its base. The understanding how the WR wind initiate is still an open issue. 相似文献
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Vasconcelos Maria Jaqueline Jatenco-Pereira Vera Opher Reuven 《Space Science Reviews》2003,107(1-2):383-386
In this work we examine the damping of Alfvén waves as a source of plasma heating in disks and magnetic funnels of young solar
like stars, the T Tauri stars. We apply four different damping mechanisms in this study: viscous-resistive, collisional, nonlinear
and turbulent, exploring a wide range of wave frequencies, from 10−5Ωi to 10−1Ωi (where Ωi is the ion-cyclotron frequency). The results show that Alfvénic heating can increase the ionization rate of accretion disks
and elevate the temperature of magnetic funnels of T Tauri stars opening possibilities to explain some observational features
of these objects.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Cool giant and supergiant stars generally present low velocity winds with high mass-loss rates. Several models have been proposed
to explain the acceleration process of these winds. Although dust is known to be present in these objects, the radiation pressure
on these particles is uneffective in reproducing the observed physical parameters of the wind. The most promising acceleration
mechanism cited in the literature is the transference of momentum and energy from Alfvén waves to the gas. Usually, these
models consider the wind to be isothermal. We present a stellar wind model in which the Alfvén waves are used as the main
acceleration mechanism, and determine the temperature profile by solving the energy equation taking into account both the
radiative losses and the wave heating. We also determine, self-consistently, the magnetic field geometry as the result of
the competition between the magnetic field and the thermal pressure gradient. As the main result, we show that the magnetic
geometry presents a super-radial index in the region where the gas pressure is increasing. However, this super-radial index
is greater than that observed for the solar corona. 相似文献
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A.A. Vidotto V. Jatenco-Pereira 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Alfvén waves have been invoked as an important mechanism of particle acceleration in stellar winds of cool stars. After their identification in the solar wind they started to be studied in winds of stars located in different regions of the HR diagram. We discuss here some characteristics of these waves and we present a direct application in the acceleration of late-type stellar winds. 相似文献
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