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References - KW32YZ
Composite hot-subdwarf binaries – I. The spectroscopically confirmed sdB sample
By: Joris Vos; Peter Nemeth; Maja Vučković; Roy H. Østensen and Steven Parsons
In: Monthly Notices of the Royal Astronomical Society - 2018 - Volume 473, Issue 1, 693-709 - 2018MNRAS.473..693V
(Astroserver project reference: KW32YZ)
Temperature, gravity, He abundance Hot subdwarfs from the UVES sample in the Teff - log(g) (upper panel) and Teff - log(nHe/nH) plane (bottom panel). The gray data points provide a reference for the subdwarf atmospheric properties and are taken from the GALEX sample. The details of our parameter determination are discussed in the paper.
Abstract:
Hot subdwarf-B (sdB) stars in long-period binaries are found to be on eccentric orbits, even though current binary-evolution theory predicts these objects to be circularised before the onset of Roche-lobe overflow (RLOF). To increase our understanding of binary interaction processes during the RLOF phase, we started a long term observing campain to study wide sdB binaries. In this article we present a composite-binary-sdB sample, and the results of the spectral analysis of 9 such systems. The grid search in stellar parameters (GSSP) code is used to derive atmospheric parameters for the cool companions. To cross-check our results and also characterize the hot subdwarfs we used the independent XTgrid code, which employs Tlusty non-local thermodynamic equilibrium models to derive atmospheric parameters for the sdB component and Phoenix synthetic spectra for the cool companions. The GSSP and XTgrid codes are found to show good agreement for three test systems that have atmospheric parameters available in the literature. Based on the rotational velocity of the companions, an estimate for the mass accreted during the RLOF phase and the miminum duration of that phase is made. It is found that the mass transfer to the companion is minimal during the subdwarf formation.

Interactive XTgrid figures [best on wide-screen]

The figures below show the observed UVES spectra (black full line) and the best fitting XTgrid composite model (red dotted line). The contribution of the cool companion is shown with a green line and the sdB contribution with a blue line. The flux is scaled so that the average continuum flux of the observed composite spectrum equals 100 for an easy comparison between the systems. Click on the panels to view the spectral decomposition in the entire UVES spectral range for each system.
Decomposition
Decomposition

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