Binaries in the FLAMES Survey of Massive Stars

The recently finished FLAMES Survey of Massive Stars allowed for the first time, through the ESO multi-object spectrograph FLAMES on the VLT, to obtain high quality spectra for a large number of hot massive main sequence (core hydrogen burning) stars. Next to rapidly rotating stars with indications for internal rotationally induced mixing (in particular surface nitrogen enhancements), this survey surprisingly found significant fractions of massive stars with unexpected properties: very slow rotators with chemically enriched surfaces, as well as evolved rapid rotators without signs of internal rotationally induced mixing. Binary evolution models have been suggested as an explanation, an our group has produced some models which could potentially explain such properties. Some of the stars with unexpected properties likely are binaries based on observed radial velocity shifts found in the multi epoch spectra. The task here is to investigate whether the constraints on orbital period and mass ratio derived from the observed radial velocity shifts are consistent, or in contradiction, with the binary evolution scenarios which could explain these observations. Furthermore, it should be tested whether the known binaries amongst the enriched rapid rotators in the FLAMES sample are consistent with the idea of rotational mixing within the single star picture.

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