Letter to the Editor
On the λ Bootis spectroscopic binary hypothesis
Institut für Astronomie der Universität Wien, Türkenschanzstr. 17, 1180 Wien, Austria e-mail: Ernst.Paunzen@univie.ac.at
Accepted: 29 August 2006
Context. 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.
Aims. 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.
Methods. 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, HD 107233 and HD 204041.
Results. 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.
Conclusions. A careful preselection of λ Bootis stars results in a homogeneous group of objects that can be used to investigate the group characteristics.
Key words: stars: chemically peculiar / stars: early-type / techniques: photometric / stars: atmospheres / stars: binaries: general
© ESO, 2006