The chromosphere and wind of the Herbig AE star, AB Aurigae.

Abstract

The Herbig Ae variable, AB Aur, has been observed with the CFHT coudé spectrograph at 95 mÅ resolution for five consecutive nights in the blue spectral region and with the lUE satellite in the high resolution, long wavelength mode. The Ca II K line shows an asymmetric and variable profile and shows weak emission in the absorption core at least some of the time. An exceptional event, characterized by the appearance of blue components in Ca II K and Balmer lines, occurred on 1980 October 26. Other evidence of chromospheric emission is the presence of the He I λ5876, and that of Mg II h and k lines which have striking P Cygni profiles. The Mg II absorption is broader (up to -380 km s^-1) than in the A supergiant α Cyg, and shows strong redward emission; the line profiles indicate mass outflow. The Balmer lines (H_δ-H₁₄) are in absorption without emission components, in contrast to observations in the 1 930s and 1 940s. Their measured averaged velocity as well as the Ca II K velocity indicate global motions, variable with time, in the atmosphere. Variability in the line profile shapes and velocities for Ca II K and the Balmer lines occurs on time scales of less than a day. The narrow components of Mg II, Ca II, and Na I which were observed are thought to arise in the nebulosity in which AB Aur is embedded. The characteristic line emission and line positions, breadth, and variability show the presence of an active and variable chromosphere with mass outflow.