On the Λ Bootis Spectroscopic Binary Hypothesis

Is the proposed spectroscopic binary model able to explain the observed abundance pattern and photometric metallicity indices for the group members? What is the percentage of undetected spectroscopic binary systems? We have 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 for single stellar atmospheres, Vega and two typical λ Bootis stars, HD 107233 and HD 204041, were generated. 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 can not explain the observations. A carefully preselection of λ Bootis stars results in a homogeneous group of objects which can be used to investigate the group characteristics. Abstract. It is still a matter of debate if the group of λ Bootis stars is homogeneously defined. A widely discussed working hypothesis formulates that two apparent solar abundant stars of an undetected spectroscopic binary system mimic a single metal-weak spectrum preventing any reliable analysis of the group characteristics.