LOOP MODELING OF CORONAL X-RAY-SPECTRA .1. GENERAL-PROPERTIES

This work is motivated by the widely accepted paradigm that the struct ure and features of stellar coronae are determined by plasma magnetica lly confined in coronal loops. In particular we address the question w hether it is possible to devise diagnostics amenable to reveal some ph ysical and geometric characteristics of static coronal loops from X-ra y observations. We show that single-loop coronal models may give spect ra differing in several respects from one- and two-temperature models, the differences being probably observable already with ASCA/SIS. We f ind that the spectra of our loop models are essentially determined by the plasma below one pressure scale height; therefore we do not need t o consider deviations from Spitzer's conductivity which occur in the v ery diluted upper atmosphere. We also find that widening of cross sect ion of the loops may give observable effects depending on loop paramet ers and that even a small fraction of the star's surface covered by co mpact coronal loops with dense plasma can easily dominate the emission from a corona and mask the emission from long and tenuous loops. Fina lly we present an example of fitting a real ROSAT/PSPC observation wit h loop-emitted spectra.