Stellar multiplicity across the mass spectrum

We investigate the multiplicity as a function of stellar mass. For this purpose we have created three complete samples of O, B, and FGK stars and performed multi-epoch, high-resolution (R ∼ 50 000) optical spectroscopy. The current results for the O-type stars suggest a multiplicity fraction of more than 80%. Many O-type systems contain components of similar mass. The multiplicity fraction for B stars seems to decrease from 70% to 20%. We argue that this general decrease is most likely due to observational biases; however, similar-mass systems – like common for O-type stars – seem to vanish toward later B-types. Within the sample of F stars we observe an increasing multiplicity fraction with primary mass (∼50% – 80%); simultaneously there is a decrease of single stars toward the A-type regime. Closer inspection of spectroscopic binaries – either by spectral disentangling or by common proper motion studies – reveals higher-level systems in each mass range