X-ray Emission Line Project

Nancy S. Brickhouse and Jeremy J. Drake

Summary. In order to make existing and forthcoming plasma codes (see Section 2) useful for X-ray spectroscopy at CCD or higher resolution, they must be improved and tested. Existing experimental benchmarks provide only weak and sparse tests. AXAF grating spectra can provide the best experimental data in atomic physics for this regime. The proposed AXAF grating calibration observations of three different stars span a sufficient test space to address known and suspected problems -- such as, an inadequate number of lines included for most species, incorrect ionization balances, and incorrect predicted line strengths even for some strong transitions. However, the minimum observation times needed to provide useful benchmark data are long, ~ 550 ks total. Lead times to complete analysis of grating observations and feedback to the spectral models are sufficiently long that the benchmark observations must be right at the very start of the mission in order to be available for AO2 proposers in March 1999. We urge the AXAF Science Center to extend the calibration observations during the on-orbit check-out period where necessary in order to obtain these vital benchmark data. The data should then be made public at once.