Search for transition zone lines in early dwarf A stars.

Abstract

The presence of hot external atmospheric layers in some A stars, demonstrated by the X-ray detections with the Einstein satellite, stimulated the search for optical counterparts, in particular, the search for the UV transition zone indicators like Si IV, C IV and He II lines. The observations of a sample of early dwarf A stars with IUE allows one to conclude that the features observed on regions of Si IV, C IV and He II lines may be explained by blends of metallic lines. In consequence, transition regions are probably not present or they have a very small thickness in dwarf A stars.