The remarkable spectral line asymmetries of F and G Ib supergiant stars

Abstract

The authors observed a group of supergiants spanning the F5 Ib to K2 Ib interval. The line asymmetries of the F supergiants are found to be large and opposite in direction from the normal case seen in cooler and less-luminous stars, and in the Sun. There is a continuous and monotonic change in the bisector behavior with spectral type, with the transition from the anomalous to the normal asymmetry occurring near G1 Ib. The authors reproduce the observations with numerical simulations based on a simple two-stream model, and from this deduce velocities of rise of the hot material to be ≡ -25 km s-1 for the F Ib supergiants.