Evolution of solar‐type stellar winds

Abstract

By extending our self-consistent MHD simulations for the solar wind, we study the evolution of stellar winds of solar-type stars from early main sequence stage to red giant phase. Young solar-type stars are active and the mass loss rates are larger by up to ∼100 times than that of the present-day sun. We investigate how the stellar wind is affected when the magnetic field strength and fluctuation amplitude at the photosphere increase. While the mass loss rate sensitively depends on the input energy from the surface because of the global instability related to the reflection and nonlinear dissipation of Alfvén waves, it saturates at ∼100 times because most of the energy is used up for the radiative losses rather than the kinetic energy of the wind. After the end of the main sequence phase when the stellar radius expands by ∼10 times, the steady hot corona with temperature 10 6 K, suddenly disappears. Chromospheric materials, with hot bubbles embedded owing to thermal instability, directly stream out; the red giant wind is not a steady stream but a structured outflow.

Spin evolution and saturation: new insights through 3D MHD simulations of young solar analogs

“…This result also strongly depends on the exponent chosen in the (T, n) laws, and more generally on how the acceleration of stellar winds depends on stellar properties. We aim to develop more physically motivated model of stellar wind acceleration (in line with Cranmer & Saar 2011;Suzuki 2013), that should be coupled with dynamo theory.…”

“…Unlike the solar wind, whose properties have been strongly constrained over the past 30 years, stellar winds remain difficult to observe. Wood et al (2005) have provided constraints on the mass loss of a dozen of solar-like stars, providing directions to transpose solar wind models in the stellar context (see Holzwarth & Jardine 2007;Cranmer & Saar 2011;Suzuki 2013). Our approach rely on the widely used polytropic wind model that can describe the acceleration of an outflow from a million Kelvin hot corona thanks to a modified adiabatic index γ close to unity (see, e.g.…”

Atmospheric Heating and Wind Acceleration in Cool Evolved Stars

“…The wave energy dissipates mostly via viscosity owing to neutral-neutral collisions and resistivity caused by ion-neutral collisions. The effect of mode coupling of the conversion of energy from Alfvén waves into slow magneto-sonic waves has also been observed and described in 1-D MHD simulations of the solar chromosphere by Lau & Siregar (1996), Torkelsson & Boynton (1998), Ofman & Davila (1997), Airapetian et al (2000) and Suzuki (2013) in simulations of solar and stellar atmospheres and winds.…”

“…Non-linear coupling of Alfvén waves excite magneto-sonic waves, which can eventually steepen into longitudinal waves that become damped by shock formation. Suzuki & Inutsuka (2005) and Suzuki (2007Suzuki ( , 2013 pursued non-linear 1.5-D MHD simulations of Alfvén wave propagation from solar and stellar photospheres into the corona. While their model does not account for cross-field gradients, they showed that non-linear Alfvén wave dissipation in the solar atmosphere can explain its thermodynamics due to the dissipation of compressible waves produced by mode coupling of non-linear Alfvén waves.…”

“…Important efforts will also consider the relevance of other kinds of processes, such as magnetic and non-magnetic chromospheric turbulence and waves, especially for low-gravity supergiants. The latter processes have the general ability to lift material closer to the critical point, and so helping to support the initiation of mass loss (e.g., Schröder & Cuntz 2005;Suzuki 2007Suzuki , 2013and references therein). Subsequent ideas and formalisms for the treatment of magnetic and non-magnetic processes for the initiation of mass loss in evolved coronal and non-coronal stars have been forwarded by Cranmer & Saar (2011) while taking stellar magnetic activity into account by extending standard indicators of age, activity and rotation to include the evolution of the filling factors of photospheric magnetic regions.…”