1999A&A...350..553B

We have conducted a high-resolution, high signal-to-noise spectroscopic survey of the members of the peculiar λ Boo stars accessible from the Canada-France-Hawaii Telescope to investigate the incidence of high-degree nonradial pulsation (NRP) in these metal-deficient stars. Of 16 objects observed more than once, 9 show conclusive evidence of such NRP, which confirms that pulsational instability is a common phenomenon in the λ Boo class. The widespread presence of NRP in the λ Boo stars indirectly supports the accretion/diffusion scenario for the formation of these objects, but unfortunately does not rule out other possible causes for the phenomena. However, extensive time-series photometry and spectroscopy of several particularly interesting pulsating members of the class noted here should provide asteroseismologists with the eigenfrequency data needed to resolve the current debate concerning the evolutionary status, and hence, the origin of these peculiar stars. From our survey, we also identify a set of four stars, including λ Boo itself, with similar fundamental parameters but remarkably different pulsation characteristic. These stars may offer vital clues as to the physical excitation of λ Boo pulsations.