STATISTICAL UNCERTAINTIES IN TEMPERATURE DIAGNOSTICS FOR HOT CORONAL PLASMA USING THE ASCA SIS

Statistical uncertainties in determining the temperatures of hot (0.5- 10 keV) coronal plasmas are investigated. The statistical precision of various spectral temperature diagnostics is established by analyzing synthetic ASCA solid-state imaging spectrometer (SIS) CCD spectra. The diagnostics considered are the ratio of hydrogen-like to helium-like line complexes of Z greater than or equal to 14 elements, line-free po rtions of the continuum, and the entire spectrum. While fits to the en tire spectrum yield the highest statistical precision, it is argued th at fits to the line-free continuum are less susceptible to atomic data uncertainties but lead to a modest increase in statistical uncertaint y over full spectral fits. Temperatures deduced from line ratios can h ave similar accuracy, but only over a narrow range of temperatures. Co nvenient estimates of statistical accuracies for the various temperatu re diagnostics are provided which may be used in planning ASCA SIS obs ervations.