Showing papers by "J. Lang published in 1993"

Electric Field Effects on Dielectronic Recombination in a Collisional-Radiative Model

Abstract: We have carried out quantal calculations for the dielectronic recombination of C 3+ in an electric field. We have used these results in a collisional-radiative model for a carbon seeded hydrogen plasma. We find that the plasma microfield increases the effective dielectronic recombination rate coefficient for C 3+ by only 40% at n H =10 9 cm −3 , for example, compared to the near factor of 3 enhancement predicted by Reisenfeld et al. in 1992. The large effects predicted by Reisenfeld et al. over a wide range of densities are the result of an over-estimation of the electric field enhancement of dielectronic recombination by their approximate calculations

The 1992 january 5 flare at 13.3-ut - observations from yohkoh

Abstract: We discuss X-ray spectra and soft X-ray images of an M1.9 flare that occurred on 1992 January 5 near 13.3 UT. These data were obtained with instrumentation on the Japanese Yohkoh spacecraft. They cover the entire rise phase of the flare. To supplement these data we have ground-based magnetograms and Halpha spectroheliograms. We calculate the electron temperature and emission measure of the flare as a function of time during the early rise phase using X-ray spectral line intensities and line ratios. Using spectral line widths, line profile asymmetries, and wavelength shifts due to the Doppler effect, we calculate the dynamical properties of the flare. The time development of the morphology of the flare, as revealed by the soft X-ray images and the Halpha spectroheliograms, and the physical quantities inferred from the X-ray spectra, are compared with chromospheric evaporation models. There is an enhancement of blueshifted emission that is closely correlated with the hard X-ray bursts. Heating of one loop in the flare is consistent with a conduction-evaporation model, but heating is found in several structures that do not appear to be physically associated with each other. No standard evaporation model can adequately explain all of the observations.