Theoretical prediction of chromospheric oscillations in late-type stars

Abstract

Self-consistent, nonlinear and time-dependent numerical computations of the excitation of chromospheric oscillations in a thin and non-isothermal magnetic flux tube embedded in magnetic-free atmospheres of late-type stars are performed. Longitudinal tube waves are considered and the wave energy spectra and fluxes generated in convective zones of these stars are calculated. The process of filtering the energy carried by longitudinal tube waves is investigated and both the local heating by shock waves as well as the excitation of chromospheric oscillations are studied. Cutoff frequencies of the resulting oscillations are computed numerically at different atmospheric heights in stars of different effective temperatures and gravities, and compared to three analytically derived cutoff frequencies. The obtained results show that the oscillation frequency ranges from 4 mHz for F5V stars to 20 MHz for M0V stars. It is pointed out that this frequency range may be relevant to the recent stellar p-mode observations made by the NASA space mission Kepler.