The Coronae of moderate-mass giants in the hertzsprung gap and the clump

摘要

We have used the Roentgensatellit(ROSAT), the Extreme Ultravilet Explorer(EUVE), and the Hubble Space Telescope(HST) to measure X-ray and ultraviolet emissions of moderate-mass (～2-3 M_⊙) Giants in the Hertzsprung gap(Spectral types early F to mid-G) and the post-helium flash " clump" (～G8-K0). Our motivation was to document the evolution of hot coronae(T > 10~6 K) along the post-main-sequence trajectories traveled by such stars in order to gain insight concerning the "X-ray deficiency" of the F-Go giants and the strong braking of stellar rotation at the red edge of the Hertzsprung gap.