Detection of further red giants with "Hybrid" atmospheres ANS a possible correlation with double circumstellar MGII and CAII lines.

Abstract

In addition to the three known hybrid atmosphere stars (Alpha and Beta Aqr, and Alpha TrA), the three red giants (Theta Her, Iota Aur and Delta TrA) which have both transition layer lines (N V, C IV, Si IV, C II) and cool winds have been detected. It is shown that all six known hybrid stars have double circumstellar Ca II and Mg II absorption lines, one high-velocity component at -70 to -140 km/sec and one low-velocity component at -5 to -20 km/sec. Together with six further stars with double circumstellar lines, these stars occupy the dividing region in the HR-diagram which separates stars with transition layer lines from stars with circumstellar lines.