The role of metals in cooling gas behind shock fronts in the atmospheres of cool stars

Continuum and line emission of flares on red dwarf stars

“…The authors fulfilled calculations of a one-dimensional radiative shock wave and demonstrated the formation of a region with a small gradient of the plasma parameters: temperature, pressure, and density (see Figures 3 and 4 in Katsova et al (1981)). This result is confirmed by the calculations of the radiative cooling behind a shock front in the atmospheres of cool stars (see Fadeyev & Gillet (2001) and Belova et al (2014)) with a more detailed account for the elementary processes in the plasma: ionization, recombination, bremsstrahlung, excitation and de-excitation of discrete levels of atoms and ions as well as radiation scattering at the frequencies of spectral lines.…”

“…The evolution of T e is caused by the balance between the supply of energy in elastic collisions with ions and atoms and radiative losses in the Lyman-α line. The radiative cooling in the hydrogen lines is the most intensive at T e ∼ 1 eV (see Belova et al (2014)). Therefore, we assume that 0.8 eV T e 1.5 eV.…”

“…The Lyman-α (Ly-α) optical depth, τ 12 , in the cooling region, as it follows from Belova et al (2014), lies in the range 1·10 7 τ 12 3·10 7 .…”

“…We use the results of the radiative shock wave calculations by Fadeyev & Gillet (2001) and Belova et al (2014) to state the input parameter set. These calculations were fulfilled under the conditions of the atmosphere of a red giant star with an effective temperature of T 0 = 3000 K. The values of T ai and T e at the shock front are respectively 7 − 10 eV and ≈ 0.7 eV.…”

Origin of the Blue Continuum Radiation in the Flare Spectra of dMe Stars

“…Fadeyev and Gillet [13], Bychkov et al [14] have calculated the profile of a stationary plane-parallel radiative shock wave with detailed accounting for elementary processes in the post-shock plasma: the electron impact ionization, the triple recombination, the electron impact excitation and de-excitation, etc. 11 The following parameters were chosen in [14] for the unperturbed gas: the total concentration of ions and atoms N 0 = 10 12 cm −3 , a temperature T 0 = 3000 K, and a magnetic field H 0 = 2 G. The magnetic field is oriented perpendicular to the gas velocity [14]. The plasma flows through the discontinuity surface at a velocity of u 0 = 60 km/s (we use a frame of reference in which the shock front is at rest).…”