Cr. Canizares et al., High-resolution X-ray spectra of Capella: Initial results from the ChandraHigh-Energy Transmission Grating Spectrometer, ASTROPHYS J, 539(1), 2000, pp. L41-L44
High-resolution spectra of the active binary Capella (G8 III + G1 III) cove
ring the energy range of 0.4-8.0 keV (1.5-30 Angstrom) show a large number
of emission lines, demonstrating the performance of the High-Energy Transmi
ssion Crating Spectrometer. A preliminary application of plasma diagnostics
provides information on coronal temperatures and densities. Lines arising
from different elements in a range of ionization states indicate that Capel
la has plasma with a broad range of temperatures, from log T = 6.3 to 7.2,
generally consistent with recent results from observations with the Extreme
-Ultraviolet Explorer and the Advanced Satellite for Cosmology and Astrophy
sics. The electron density is determined from He-like O VII lines, giving t
he value of Ne similar to 10(10) cm(-3) at T-e similar to 2 x 10(6) K; He-l
ike lines formed at higher temperatures give only upper limits to the elect
ron density. The density and emission measure from O VII lines together ind
icate that the coronal loops are significantly smaller than the stellar rad
ius.