  High resolution X-ray spectroscopy with the diffraction gratings of Chandra
and XMM-Newton offers new chances to study a large variety of stellar coronal
phenomena. A popular X-ray calibration target is Capella, which has been
observed with all gratings with significant exposure times. We gathered
together all available data of the HETGS (155ks), LETGS (219ks), and RGS (53ks)
for comparative analysis focusing on the NeIX triplet at around 13.5A, a region
that is severely blended by strong iron lines. We identify 18 emission lines in
this region of the HEG spectrum, including many from FeXIX, and find good
agreement with predictions from a theoretical model constructed using the
Astrophysical Plasma Emission Code (APEC). The model uses an emission measure
distribution derived from FeXV to FeXXIV lines. While these 18 emission lines
cannot be isolated in the LETGS or RGS spectra, their wavelengths and fluxes as
measured with HEG are consistent with the lower resolution spectra. In the
Capella model for HEG, the weak intercombination line of NeIX is significantly
blended by iron lines, which contribute about half the flux. After accounting
for blending in the He-like diagnostic lines, we find the density to be
consistent with the low density limit (n_e<2 10^10 cm^-3); however, the
electron temperature indicated by the NeIX G-ratio is surprisingly low (~2MK)
compared with the peak of the emission measure distribution (~6MK). Models show
that the NeIX triplet is less blended in cooler plasmas and in plasmas with an
enhanced neon-to-iron abundance ratio.
