High-resolution X-ray spectroscopy of late-type stars with CHANDRA Original Research Article

We have analyzed high-resolution (Δλ ≅ 0.06 Å) X-ray spectra in the region 6–180 Å of the coronae of the cool stars Capella, Procyon, and α Centauri. These stars were observed with the the CHANDRA Low Energy Transmission Grating Spectrometer (LETGS) between Sep. and Dec. 1999. Temperatures are derived from line ratios of helium-like lines and long-wavelength iron lines. Electron densities are obtained for the relatively cooler (few MK) and more tenuous (⪅ 1011 cm−3) plasma components from the forbidden to intercombination line ratios in the helium-like triplets of O, N, and C and for the hotter (⪆ 5 MK) and denser (⪆ 1012 cm−3) components (such as occur in Capella) from the helium-like triplets of Mg and Si and the ratios of Fe XIX-Fe XXII 2ℓ-2ℓ′ lines above 90 Å. The implications of these results for the coronal structure are discussed.