Model Issues - I
Absorption cross-sections.The cross-sections used in the current models for photoelectric absorption are no longer adequate.
At grating and calorimeter resolutions the edges are not single sharp changes in cross-section. At these resolutions we are also sensitive to changes in ionization state of the absorbing material so we need an accurate model of the ISM.
We have added Verner's cross-sections (which include all ionization states) and will be adding a high resolution model of the oxygen edge. An accurate model for the ISM is still to be calculated.
Collisional plasma models suffer some of the same problems as those for photoelectric absorption. The Raymond-Smith model should not be used with high-resolution data - it was never intended for that purpose. The Mewe-Kaastra-Liedahl model can be used but only with the switch=0 (calculate) option.
When it is released the new APED-based code (cf poster by Brickhouse, Smith & Houck) will be included in XSPEC.
We will also extend the definition of the table model file to allow the continuum and lines to be stored separately. This will allow the tabulated model to be redshifted safely when used with high resolution data.