Longitudinal magnetic tube wave fluxes in stars of low metallicity

Abstract

A modified theory of turbulence generation is combined with the magnetohydrodynamic equations to numerically compute the wave energies generated at the base of magnetic flux tubes for stars with effective temperatures ranging from Teff= 3000 to 7000 K, gravity log g= 4.44 and with different metal abundances: solar, 0.1, 0.01 and 0.001 of solar metallicity. The results show that the effect of metallicity is very important for cool stars (Teff < 5500 K). The current numerical approach allows for non‐linear waves with large amplitudes and thus the obtained results for time‐averaged wave energy fluxes are higher than those obtained by the analytical approach. For hot stars the effect is negligible. The computed energy fluxes are essential for constructing theoretical models of the magnetic chromosphere of low‐metallicity stars. The maximum obtained wave energy flux for low‐metallicity stars is about 7.3 × 108 erg cm−2 s−1.

Solar magnetic flux tube simulations with time-dependent ionization

“…attainment of radiative equilibrium, position of optical depth τ 5000 ). Previous work by Ulmschneider et al (2001) adopted the opacity tables compiled by Bohn (1984) and Ulmschneider et al (1996), whereas more recent simulations (Fawzy 2010) use the opacity table given by R. L. Kurucz and collaborators (see Castelli & Kurucz 2004 for details).…”

“…There is also considerable previous work on the most appropriate value for the initial wave energy flux of longitudinal tube waves; the latter is also modestly affected by the solar photospheric opacities owing to their influence on the construction of the solar tube models (i.e., attainment of radiative equilibrium, position of optical depth τ5000). Previous work by Ulmschneider et al (2001) adopted the opacity tables compiled by Bohn (1984) and Ulmschneider et al (1996), whereas more recent simulations (Fawzy, 2010) use the opacity table given by R. L. Kurucz and collaborators (see Castelli & Kurucz 2004 for details). This latter approach is adopted in the present paper.…”

Generation of longitudinal flux tube waves in theoretical main-sequence stars: effects of model parameters

“…It requires specifying the strength of the magnetic field inside the flux tube and the height in the stellar atmosphere where the squeezing is assumed to take place. The code has previously been used to calculate wave energy fluxes and spectra for longitudinal tube waves propagating in the solar atmosphere (see Fawzy et al 1998, for models of different spreading factors), and to investigate the dependence of these fluxes on the magnetic field strength, the rms velocity amplitude of turbulent motions, and the location of the squeezing in the atmosphere; for models of stars with non-solar metallicities, we refer to Fawzy (2010).…”