The UV spectrum as a signature of the lambda Bootis character.

Abstract

The spectra of all the stars previously classified as Lambda Bootis stars and observed by the IUE satellite at low resolution, in the short wavelength range, are analyzed. The usefulness of this spectral range for classifying the Lambda Boo stars is shown; the UV criteria used to distinguish the Lambda Boo stars from other metal-deficient stars are selected and applied. The origin of the Lambda Boo phenomenon is not yet clear (Baschek and Slettebak, 1988) and a careful selection of the candidates is the first step for a clear definition of the theoretical problem. From the present study, it turns out that only seven out of the 19 candidates can be assigned to the Lambda Boo group, while for the other stars the previous classification must be considered eroneous. The peculiarities of the other metal-deficient, but not Lambda Boo, stars are discussed.