The Effects of Alfven Waves and Radiation Pressure in Dusty Winds of Late‐Type Stars. II. Dust‐Cyclotron Damping

Abstract

There are in the literature several theories to explain the mass loss in stellar winds. In particular, for late-type stars, some authors have proposed a wind model driven by an outward-directed flux of damped Alfvén waves. The winds of these stars present great amounts of dust particles that, if charged, can give rise to new wave modes or modify the preexisting ones. In this work, we study how dust can affect the propagation of Alfvén waves in these winds, taking into account a specific damping mechanism, dust-cyclotron damping. This damping affects the Alfvén wave propagation near the dust-cyclotron frequency. Hence, if we assume a dust size distribution, the damping occurs over a broad band of wave frequencies. In this work, we present a model of Alfvén wave-driven winds using the dust-cyclotron damping mechanism. On the basis of coronal holes in the Sun, which present a superradial expansion, our model also assumes a diverging geometry for the magnetic field. Thus, the mass, momentum, and energy equations are obtained and then solved in a self-consistent approach. Our results of wind velocity and temperature profiles for a typical K5 supergiant star show compatibility with observations. We also show that, considering the presence of charged dust particles, the wave flux is less damped due to dust-cyclotron damping than it would be if we were to consider some other damping mechanisms studied in the literature, such as nonlinear damping, resonant surface damping, and turbulent damping.

Temporal variations of the outer atmosphere and the dust shell of the carbon-rich Mira variable V Ophiuchi probed with VLTI/MIDI

“…We also note that the mass loss rate of V Oph is of the order of 10 −8 M yr −1 , which is by two orders of magnitude lower than that of S Cep. It is necessary to compare with dynamical models computed with parameters corresponding to V Oph for a better understanding of the physical processes responsible for molecule and dust formation close to the star: whether the extended C 2 H 2 layers can be explained by dust-driven winds triggered by large-amplitude stellar pulsation alone or some other mechanism is operating such as Alfvén wave-driven winds (e.g., Vidotto & Janteco-Pereira 2006;Suzuki 2006). …”

Evolution of atmospheric escape in close-in giant planets and their associated Ly α and H α transit predictions

“…energy and momentum. To achieve convergence of the wind solution, we use a shooting method based on the model of Vidotto & Jatenco-Pereira (2006).…”

Alfvén waves in space and astrophysical dusty plasmas

“…In the case of ω min < ω < ω max , the integral in the particle radii has singularities, whose residues give the complex part of the wave number (k z ≡ k R + ik C ) and lead to the dust-cyclotron damping of the waves, with damping length L ≡ L(ω) = 2π /k C (ω). If we consider a distribution of grain sizes, the waves are damped in a broad band of resonance (Vidotto and Jatenco-Pereira, 2006).…”

“…Since it is observed that the winds of late-type supergiant stars contain significant amounts of dust, the Alfvén waves can be dissipated in these winds. In order to evaluate how this damping mechanism can accelerate the wind, Vidotto and Jatenco-Pereira (2006) proposed a model that considers an outward flux of Alfvén waves generated at the stellar surface that is damped only due to the interaction with dust grains. They studied a K5 supergiant star with the following magnetic field configuration: from the surface, the magnetic field configuration is divergent and after a transition radius r t , it becomes radial.…”

“…The mass, energy, and momentum equations, which were solved simultaneously by taking into account both the radiative losses and the wave heating in the energy equation, determine the temperature. Vidotto and Jatenco-Pereira (2006) assumed that the wave energy density is dissipated as follows:…”