Extreme-ultraviolet transition-region line emission during the dynamic formation of prominence condensations

We calculated the emission expected in EUV transition-region lines during t he process of dynamic formation of prominence condensations in coronal loop s, as predicted by the thermal nonequilibrium model of Antiochos et al. We selected some lines emitted by ions of carbon and oxygen because they are a mong the most intense and representative in the temperature range correspon ding to the solar transition region. We present and discuss the principal c haracteristics of the line intensities and profiles synthesized from the hy drodynamic model at different times during the loop evolution. The ionizati on balance is computed in detail and the deviations from the ionization equ ilibrium caused by plasma flows and variations of temperature and density a re accounted for. The atomic physics is treated using the latest atomic coe fficients and the collisional-radiative theory approach. The synthesized ca rbon and oxygen lines exhibit a behavior significantly dependent on the var iations of the plasma parameters inside the magnetic flux tube and therefor e are suitable observational signatures of the processes giving rise to pro minence condensations. In particular, a sizeable increase of line intensity as well as small blueshifts are expected from the loop footpoints during t he first part of the evaporation phase that fills the loop with the materia l which subsequently condenses into the prominence. Once the condensation a ppears, line intensities decrease in the footpoints and simultaneously incr ease at the transition regions between the cool plasma of the condensation and the coronal portion of the loop. Line shifts are quite small in our sym metric model, and during most of the condensation's lifetime, the nontherma l widths are relatively small. These results can be compared with detailed ultraviolet observations of filament/prominence regions obtained by recent space missions in order to test the model proposed for the formation of sol ar prominences.