CHANDRA-LETGS X-ray observations of Capella - Temperature, density and abundance diagnostics

We report an analysis of the X-ray spectrum of Capella from 6 to 175 Angstr om obtained with the Low Energy Transmission Grating Spectrometer (LETGS) o n board of the X-ray space observatory CHANDRA. Many emission line features appear that can be resolved much better as compared to former instruments (EUVE and ASCA). Coronel electron densities (n(e)) and temperatures (T) of brightly emitting regions are constrained by an analysis of ratios of densi ty- and temperature-sensitive lines of helium-like ions and highly ionized iron atoms. Lines emitted by e.g., O VII & VIII, Mg X-XII, Si XII-XIV, Fe I X, X & XV-XXIII are used to derive T. Line ratios in the helium-like triple ts of C V, N VI, O VIE, Mg XI, and Si XIII yield T in the range 0.5-10 MK, and n(e) in the range 10(9)-10(13) cm(-3). The Fe IX/X ratio yields T simil ar or equal to 0.9 MK, while lines from Fe XVIII to XXII give T similar to 6-10 MK. Flux ratios of Fe XX-XXII lines indicate for the electron densitie s an upper limit in the range n(e) less than or similar to (2-5) 10(12) cm( -3). From line ratios of Fe XVII and Fe XVIII we derive constraints on the optical depth tau of similar to1-1.5. An emission measure distribution is d erived from Fe line intensities. Results for element abundances (relative t o Fe) from a 4-T model are: O and Ne/Fe about solar, N, Mg and Si/Fe simila r to 2x solar. The results for T and n(e) are described in terms of quasi-s tatic coronal loop models and it is shown that the X-fay emission originate s from compact structures much smaller than the stellar radii.