The Fe IX Line at 17.1 nm in the Radiation Spectrum of Slow Magneto-Acoustic Waves Propagating in the Solar Corona

Abstract

Profiles of the Fe IX line at a wavelength of λ = 17.1 nm in the radiation spectrum of slow magneto-acoustic waves, propagating in coronal loops, are calculated under conditions of an optically thin layer and a constant density. The parameter values used in calculations of the line profiles are as follows: the amplitude of the velocity of particles’ displacements in a wave v₀ = 10 km/s, the width of the coronal loop is 2000 and 5000 km, the wavelength Λ = 20 000 km and 50 000 km, and the value of the Doppler width Δλ_d = 1 pm; the values for the angle of view and the wave phases were varied. The true value of the energy flux density is 622 erg/cm²s. The values of the energy flux density obtained in calculations strongly depend on the angle of view θ and the wave phase: they range from 0 and, when the values of θ are large, to 2000 erg/cm²s. The values of the Doppler velocities v_d and the velocities of nonthermal motions v_nt take maximal values of ~12 km/s at small angles θ and almost vanish at large angles θ. When the angle of view is small (θ < 30°), a weak blue asymmetry is noticeable. When the angle of view is large (θ > 30°), the asymmetry is almost invisible.