TEMPERATURE DEPENDENCE OF EMISSION MEASURE IN SOLAR X-RAY PLASMAS I - Non-Flaring Active Regions

摘要

X-ray and ultra-violet line emission from hot, optically thin material forming coronal active regions on the sun may be described in terms of an emission measure distribution function, φ(T) = ne2 dV/dT. We develop the relationship between line flux and φ(T), a theory which assumes that the electron density is a single-valued function of temperature. The sources of error involved in deriving φ(T) from a set of line fluxes are examined in some detail. These include errors in atomic data (collisional excitation rates, assessment of other mechanisms for populating excited states of transitions, element abundances, ion concentrations, oscillator strengths) and errors in observed line fluxes arising from, e.g., poorly - known in¬strumental responses. We discuss two previous analyses in which φ(T) for a non-flaring active ragion is derived. A least-squares method of Batstone et_al. uses x-ray data of low statistical significance, a fact which appears to influence their results considerably.