One-dimensional nonideal magnetohydrodynamic simulations of non-coronal K-giant atmospheres (Arcturus, Aldebaran) show that Alfven waves excited by surface convection drive the stellar wind, but because the atmosphere is only partially ionized, ambipolar diffusion damps the waves and reduces the time-averaged mass-loss rate by more than an order of magnitude relative to ideal MHD, bringing it into agreement with the observed ~1e-11 solar masses per year. The simulations further predict that radiative-cooling-driven thermal instability makes hot magnetized bubbles (>1e6 K, emitting soft X-rays) coexist with cool molecular gas, and that the mass-loss rate depends sensitively on magnetic field strength and metallicity through the ambipolar diffusion.
Astrophysics primary-research paper (Suzuki, Ohnaka & Yasuda; accepted PASJ). Using 1D nonideal-MHD simulations in super-radially open flux tubes, the authors model Alfven-wave-driven winds from the …