Magnetic wave energy fluxes for late-type stars

Abstract

Abstract. The wave energy fluxes carried by longitudinal tube waves along thin vertical magnetic flux tubes embedded in atmospheres of late-type stars are computed. The main physical process responsible for the generation of these waves is the nonlinear time-dependent response of the flux tubes to continuous and impulsive external turbulent pressure fluctuations, which are represented here by an extended Kolmogorov spatial and modified Gaussian temporal energy spectrum. Both the wave energy fluxes and spectra are calculated for population I stars with effective temperatures ranging from T eff = 3500 K to 7000 K, and with gravities in the range log g = 3−5. The obtained results show that the computed wave energy may significantly contribute to the enhanced heating observed in magnetic regions of late-type stars.

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

“…5 for details. This behaviour was also pointed out by Ulmschneider et al (2001). Moreover, we find that the wave energy flux for upwardly propagating waves is also somewhat sensitive to the choice of α for the stellar convective zone.…”

“…For the Sun, adopted a variety of observed rms velocity amplitudes u t in the range 0.9 < u t < 1.9 km s −1 , and illustrated the dependence of the computed fluxes on this velocity. For stars, these velocities cannot be determined from observations; thus, we follow Ulmschneider et al (2001) and v CMax (see Fig. 2) are evaluated from stellar convection zone models based on the adopted mixing length parameter.…”

Excitation of transverse magnetic tube waves in stellar convection zones

“…These models require the initial wave energy fluxes to be specified at the atmospheric height where the calculations begin: the bottom of the chromosphere or the wind base. We have calculated the energy fluxes carried by acoustic waves (Musielak et al 1994;Ulmschneider et al 1996Ulmschneider et al , 1999 and longitudinal tube waves (Musielak et al 1989Musielak et al 2000;Ulmschneider et al 2001b) and used them to construct our stellar chromospheric models. The amount of energy carried by transverse tube waves has been added ad hoc in these models (see Ulmschneider et al 2001a).…”

“…We now use the results of Paper I to compute the transverse tube wave energy spectra and fluxes generated in convection zones of population I stars with effective temperatures ranging from T eff = 2000 K to 10 000 K, and with gravities in the range: log g = 3-5. While performing the calculations, we have carefully identified those regimes where our current model cannot be applied because of the failure of the small Mach number approximation (see Ulmschneider et al 2001b and their Fig. 1).…”

Heating of Stellar Chromospheres and Transition Regions

“…Because of the difference in these two approaches, the analytically and numerically calculated fluxes can be seen as lower and upper bounds for the realistic stellar wave energy fluxes. The numerical approach has been used by Ulmschneider et al (2001b) to calculate the amount of energy carried by longitudinal tube waves in atmospheres of selected late-type dwarfs and subgiants. Since the calculations have been performed only for a narrow range of Teff' the numerical wave energy fluxes are not included in Fig.…”