2006A&A...458L..17S

It is still a matter of debate whether the group of λ Bootis stars have been homogeneously defined. A widely discussed working hypothesis postulates that two apparent, solar-abundant stars of an undetected spectroscopic binary system mimic a single metal-weak spectrum thus preventing any reliable analysis of the group characteristics. We investigate whether the proposed spectroscopic binary model can explain the observed abundance pattern as well photometric metallicity indices and what the percentage of undetected spectroscopic binary systems is. We used the newest available stellar atmospheres to synthesize 105 hypothetical binary systems in the relevant astrophysical parameter range. These models were used to derive photometric indices. As a test, values were generated for single stellar atmospheres, Vega and two typical λ Bootis stars, HD107233 and HD204041. The synthesized indices fit the standard lines and the observations of the three stars excellently. For about 90% of the group members, the spectroscopic binary hypothesis cannot explain the observations. A careful preselection of λ Bootis stars results in a homogeneous group of objects that can be used to investigate the group characteristics.