Browsing by Author "Musielak, Z. E."

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Citation - WoS: 16
Citation - Scopus: 17
Atmospheric Oscillations in Late-Type Stars - I. Non-Linear Response To Excitation by Acoustic Wave Energy Spectra
(Wiley-Blackwell, 2012) Fawzy, Diaa E.; Musielak, Z. E.
The main aim of this paper is to perform first self-consistent numerical computation of the response of stellar atmospheres to the propagation of acoustic waves specified by realistic acoustic wave energy spectra. In the numerical approach, stellar atmospheres are stratified, non-isothermal and plane-parallel, and only their magnetic-free regions are considered. The resulting atmospheric heating is calculated and the time sequence of atmospheric velocities computed by a time-dependent hydrodynamic numerical code is analysed. All computations are done adiabatically and Fourier analysis is used in order to determine the oscillatory properties of stellar atmospheres. The numerical approach is supplemented by an analytical treatment in which three different local acoustic cut-off frequencies are selected from the literature; their values in the stellar atmospheric models are calculated and compared to the numerical results. The theoretical results obtained clearly show that atmospheric oscillations do exist in late-type stars and that their origin and physical properties are similar to those observed in the solar atmosphere. The oscillation frequency of stellar atmospheric oscillations ranges from 7.5 mHz for F5V stars to 16.0 mHz for M0V stars. The relevance of this theoretically predicted range of stellar oscillation in solar-like stars to the recent data obtained by the NASA space mission Kepler is discussed.
Citation - WoS: 2
Citation - Scopus: 3
Theoretical Prediction of Chromospheric Oscillations in Late-Type Stars
(Springer, 2016) Fawzy, Diaa E.; Musielak, Z. E.
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.