A New Synthetic XUV Spectrum

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Session 112 -- Models and Synthetic Spectroscopy
Display presentation, Saturday, January 15, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[112.03] A New Synthetic XUV Spectrum

K. P. Dere, H. E. Mason, B. C. Monsignori Fossi, K. H. Waljeski (NRL, U. Cambridge, Arcetri, NRL/NRC)

We have begun a program to develop a synthetic XUV spectrum for the 70 - 2500 /AA wavelength region based on a critical analysis of the most recent calculations of atomic parameters, in particular, atomic collision strengths and their thermal averages. Ultraviolet spectra returned by the EUVE and HST instruments demonstrate a continued need for the most accurate atomic parameters in order to determine the physical conditions in the emitting plasmas. Most previous synthetic spectra has relied heavily on the gaunt factor approximation which can predict excitation rates only for dipole transitions and only to within a factor of 2 to 3. In many cases, direct calculations of the collision strengths are now available. Burgess and Tully (1992) have developed a technique for critically evaluating collision strength calculations and scaling and compacting the data. Different scalings are available for resonance, intercombination and forbidden excitations. This method will be applied in the construction of our spectrum. In the end, we intend to produce a set of critically evaluated atomic parameters from which the nearly optically thin spectrum of a low density astrophysical plasma can be calculated, together with the programs necessary to perform these calculations. We will include the ability to prescribe elemental abundances and to correct for optical depth and populations of metastable levels as a function of density. The data sets and programs will be made available by anonymous ftp.

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