The heterogeneous class of λ Bootis stars ^*,**

¹ Institut d'Astrophysique, 98bis Bd. Arago, 75014 Paris, France
² Lab. Astronomie, Bât. 470, Université de Paris Sud XI, 91405 Orsay Cedex, France
³ Dipartimento di Astronomia, Università degli Studi di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy e-mail: faraggiana@ts.astro.it
⁴ Canada-France-Hawaii Telescope (CFHT) Corporation, Kamuela, HI 96743, USA e-mail: lai@cfht.hawaii.edu

Corresponding author: M. Gerbaldi, gerbaldi@iap.fr

Received: 10 June 2003
Accepted: 12 September 2003

Abstract

We demonstrate that it is arduous to define the λ Boo stars as a class of objects exhibiting uniform abundance peculiarities which would be generated by a mechanism altering the structure of their atmospheric layers. We collected the stars classified as λ Boo up to now and discuss their properties, in particular the important percentage of confirmed binaries producing composite spectra (including our adaptive optics observations) and of misclassified objects. The unexplained RV variables (and thus suspected binaries), the known SB for which we lack information on the companion, the stars with an UV flux inconsistent with their classification, and the fast rotating stars for which no accurate abundance analysis can be performed, are also reviewed.