Composite Hot Subdwarf Binaries - I. The Spectroscopically Confirmed Sdb Sample

Hot subdwarf-B (sdB) stars in long-period binaries are found to be on\neccentric orbits, even though current binary-evolution theory predicts these\nobjects to be circularised before the onset of Roche-lobe overflow (RLOF). To\nincrease our understanding of binary interaction processes during the RLOF\nphase, we started a long term observing campaign to study wide sdB binaries. In\nthis article we present a composite-binary-sdB sample, and the results of the\nspectral analysis of 9 such systems. The grid search in stellar parameters\n(GSSP) code is used to derive atmospheric parameters for the cool companions.\nTo cross-check our results and also characterize the hot subdwarfs we used the\nindependent XTgrid code, which employs Tlusty non-local thermodynamic\nequilibrium models to derive atmospheric parameters for the sdB component and\nPhoenix synthetic spectra for the cool companions. The independent GSSP and\nXTgrid codes are found to show good agreement for three test systems that have\natmospheric parameters available in the literature. Based on the rotational\nvelocity of the companions, an estimate for the mass accreted during the RLOF\nphase and the miminum duration of that phase is made. It is found that the mass\ntransfer to the companion is minimal during the subdwarf formation.\n