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We have reanalyzed the numerous high resolution observations of Capella (G8 III + G0 III) made by the SWP camera of the International Ultraviolet Explorer (IUE) in its 16 year lifetime. One of our goals was to search for long term profile variations in Capella's ultraviolet emission lines, but we were unable to find any compelling evidence for any significant variations. Another goal is to compare the line profiles observed by the IUE with those observed by the Goddard High Resolution Spectrograph aboard the Hubble Space Telescope.
Previous authors have shown that the G8 star is only a minor contributor to the high excitation transition region lines, but is a significant contributor to the low excitation chromospheric lines. We have found exceptions to this rule, however. We find that the G8 star is responsible for a large portion of Capella's N~V $\lambda\lambda$1238, 1242 emission, but is not a large contributor to the chromospheric S~I $\lambda$1295, Cl~I $\lambda$1351, and O~I] $\lambda$1355 lines, and we suggest possible explanations for this. We also find evidence that the He~II $\lambda$1640 emission from the G0 star is from the transition region, while the He~II $\lambda$1640 emission from the G8 star is chromospheric. The C~II $\lambda$1335 line shows a weak central reversal. We have modeled this line with Gaussians, and we find that the Gaussian representing the central reversal is blueshifted by about 9 km s$^{-1}$ with respect to the Gaussian representing the emission from the G0 star, similar to the central reversal observed in the solar C~II $\lambda$1335 line.
