SELF-CONSISTENT AND TIME-DEPENDENT MAGNETOHYDRODYNAMIC CHROMOSPHERE MODELS FOR MAGNETICALLY ACTIVE STARS

We present self-consistent and time-dependent MHD heating models for c hromospheres of magnetically active stars. We investigate the propagat ion and dissipation of longitudinal flux-tube waves in K2 V stars with different rotation rates implying different photospheric and chromosp heric magnetic filling factors. These filling factors are critical for determining the number of flux tubes on the stellar surface and the s preading of the tubes with height, which is relevant for the propagati on and dissipation of the magnetic energy as well as the generated rad iative emission losses. The filling factors used in this Letter are es timated using a relationship between the photospheric values for B(o)f (o) and P-rot in accord with very recent magnetic field measurements b y Ruedi et al. We also consider revised computations of magnetic energ y fluxes by Ulmschneider & Musielak generated by turbulent motions. Ou r models show increased shock strengths and energy dissipation rates i n stars of faster rotation because of the narrower spreading of the tu bes. This also leads to increased chromospheric emission, particularly in Mg II in stars of faster rotation. We consider these results as a first step toward a theoretical derivation of chromospheric emission-s tellar rotation relationships for stars of different masses and evolut ionary status.