Extreme ultraviolet spectroscopy of Capella

The X-ray active binary system Capella was observed with a moderate-resolution extreme ultraviolet spectrograph from 200 to 330 A. Two low-level emission features were detected. One most likely is geocoronal He II 304 A emission, while the other probably originates from the corona of Capella. The weak stellar emission at 304 A is in direct conflict with predictions of the intrinsic stellar He II flux based on standard scaling arguments but is consistent with the only previous observation of Capella in the EUV. The most plausible explanation for the lack of stellar 304 A emission is a warm wind from the active G0 III star.