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

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.