Ionization equilibrium in soft X-ray-emitting solar flares

Studies of the flare-produced line feature at 1.9 Å due to highly ionized iron show that it is emitted in conditions closely approximating steady-state ionization equilibrium. Calculations of the line flux per unit emission measure from time-dependent and steady-state ionization equilibria are compared with observed values during four flares in particular. Only for electron densities N _e 10¹⁰ cm^-3 do the time-dependent equilibrium values give as good an approximation to the observed values as the steady-state equilibrium. This lower limit is compared with values of N _e derived from analyses of the temperature decline in each of these events, and with estimates of N _e given by other workers.NAS/NRC Research Associate.