HIGH-RESOLUTION MEASUREMENT OF THE K-ALPHA-SPECTRUM OF FE-XXV-XVIII -NEW SPECTRAL DIAGNOSTICS OF NONEQUILIBRIUM ASTROPHYSICAL PLASMAS

We present laboratory measurements of high-resolution spectra of iron I(a emission under transient ionization conditions similar to those th at are believed to exist in stellar flares and young supernova remnant s. Taking advantage of our high spectral resolution (lambda/Delta lamb da greater than or equal to 2000, we identify a number of transitions that can serve as diagnostics of ionizing plasmas. By varying the exci tation energy in the experiments, we constrain the effects of the elec tron distribution on these diagnostic lines. Using our measured line r atios, we deduce values for the ionization time, eta= N(e)t, in the pl asma, which agree with the actual values to similar to 20% accuracy. T his result gives us confidence to our ability to derive similar constr aints on astrophysical plasmas from remote X-ray spectroscopic observa tions.