Abstract
Spectroscopic observations of the ecllpsing variable AU Monocerotis at the Cerro Tololo Inter-American Observatory in January, 1979 suggested a behavior of the system that is completely different from the behavior that had been reported from observations made in 1944, and, more recently, on the basis of the Ha emission. The new observations suggest that: a) The B5 primary component is characterized by a surface activity that shows erratic velocity variations that amount to as much as 75 km 1 on consecutive plates, and by ejecting relatively hot gas (since the effect is seen in He I) with perhaps a sort of spherical symmetry. b) The F0 companion ejects cooler gas in all directions. c) There is a concentration of matter between the two stars. The lUE ultraviolet spectrum of AU Mon displays only absorption features that can be classified in different groups, each group would originate in a different region of the envelope that surrounds the system. So far, we have been able to establish four groups of lines and we place the regions responsible for them in the following order, going from the outermost layers towards the close pair: 1) Zero or low excitation sharp, deep lines of neutral `and singly ionized elements produced in a circumstellar region; some of these lines may be of interstellar origin, 2) Broad resonance lines of N V, Si IV that suggest a maximum of the excitation temperature Te at some distance from the stars, in a region of relatively low density and where turbulence must be at work. 3) High excitation transitions of ions like Fe III, C III, Si III. 4) Lines that may be of stellar origin.
