1998A&A...329..155P

We report the discovery of two new λ Bootis-type spectroscopic binary systems (HD 84948 and HD 171948). High resolution spectra were analyzed in order to derive abundances as well as astrophysical quantities. It resulted in extreme (HD 171948) and moderate (HD 84948) underabundances of Na, Mg, Si, Ca, Sc, Ti, Cr and Fe with respect to the Sun, thus establishing all four individual stars as true members of the λBootis group. These two systems are therefore the first spectroscopic binary systems where both components are λ Bootis-type stars. Furthermore, we have discovered δ Scuti type pulsation for one component of HD 84948 making this star particularly interesting for further observations. Since many authors have used the rotational velocity for discriminating λBootis stars (vsini>50km/s), we note that both components of HD 171948 are the slowest (vsini<20km/s) rotating λ Bootis-type stars known so far. Using the Hipparcos data, we are able to rule out the diffusion/mass-loss mechanism as origin for these two systems. Pre- as well as Main Sequence evolutionary tracks for the age determination yield consistent results with the predictions of the diffusion/accretion theory, establishing both systems as being very close to the Main Sequence. A determination of the orbital elements and/or an asteroseismological investigation of HD 84948 could provide an independent proof of our results.