The corona of the G-type giant HR 2554: discovery of co-existing, very different temperature regimes.

Abstract

We present direct observational evidence for two different co-existing coronal temperature regimes in the ζ Aur-type binary HR 2554 (G7II + A1V). ROSAT observations reveal the presence of plasma at temperatures around 10^6.7^K, typical of coronal plasma found in giants, while IUE observations, taken during egress from eclipse, show circumstellar (CS) C IV and Si IV absorption lines in the spectrum of the secondary, which reveal a significant amount of geometrically extended (0<h<1R*) plasma in the temperature regime of about 10^5^K, similar to that found in HR 6902.