Detection of X-ray Resonance Scattering in Active Stellar Coronae

An analysis of Lyman series lines arising from hydrogen-like oxygen and neon ions in the coronae of the active RS CVn-type binaries II Peg and IM Peg, observed using the {\it Chandra} High Resolution Transmission Grating Spectrograph, shows significant decrements in the Ly$\alpha$/Ly$\beta$ ratios as compared with theoretical predictions and with the same ratios observed in similar active binaries. We interpret these decrements in terms of resonance scattering of line photons out of the line-of-sight; these observations present the first strong evidence for this effect in active stellar coronae. The net line photon loss implies a non-uniform and asymmetric surface distribution of emitting s…