A comparison of three solar active regions based on their soft X-ray line spectra

A rocket-borne, collimated spectrometer has obtained the soft X-ray (1.0–2.2 nm) spectra of three solar active regions. The principal features of the spectra are described and are then used to determine the conditions in the active regions. An isothermal (single temperature) model is not able to describe the observed spectra so that a continuous distribution of emission measure with temperature is introduced.This distribution, based on that proposed by Chambe, is then used to investigate the structure of the active regions. Several simple models are considered. It is shown that each active region has a hot, dense core surrounded by a large outer volume through which the temperature and density fall until normal coronal conditions are reached.Two of the regions exhibited similar characteristics with the cores having electron densities 10¹⁰ cm^–3 and temperatures of at least 4 × 10⁶K. Even the third region, which was much less impressive and quite compact in H, appears to have had a small amount of this dense plasma in its central core.