λ Bootis stars: Current status and new insights from Spitzer

The group of λ Bootis type stars comprises late B- to early F-type, Population I objects which are basically metal weak, in particular the Fe group elements, but with the clear exception of C, N, O and S. We present a spectroscopical definition for the group membership by using the light element versus metal abundance pattern. One of the current explanations for the λ Bootis peculiarity is the accretion of interstellar material as the star travels through a diffuse interstellar cloud. We will review this hypothesis in the context of ESO high resolution spectra and Spitzer imaging and photometry. The Na I D lines provide simultaneously stellar abundances and physical properties of interstellar material along the line of sight. The new Spitzer results shed light on the presence of dust around these stars, its composition and geometric distribution.