Volume 628, August 2019
|Number of page(s)||16|
|Section||Stellar structure and evolution|
|Published online||30 July 2019|
Modelling of the B-type binaries CW Cephei and U Ophiuchi
A critical view on dynamical masses, core boundary mixing, and core mass
Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
2 Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10000 Zagreb, Croatia
Accepted: 15 May 2019
Context. Intermediate-mass stars are often overlooked. They are not supernova progenitors, but still host convective cores and complex atmospheres that require computationally expensive treatment. This means that there is a general lack of this class of stars modelled by state-of-the-art stellar structure and evolution codes.
Aims. We used high-quality spectroscopy to update the dynamically obtained stellar parameters and to produce a new evolutionary assessment of the bright B0.5+B0.5 and B5V+B5V binary systems CW Cep and U Oph.
Methods. We used new spectroscopy obtained with the Hermes spectrograph to revisit the photometric binary solution of the two systems. The updated mass ratio and effective temperatures are incorporated to obtain new dynamical masses for the primary and secondary. With these data we performed evolutionary modelling using isochrone-clouds to investigate the core properties of these stars.
Results. We report the first abundances for CW Cep and U Oph, and we report an updated dynamical solution for the two systems. We find that we cannot uniquely constrain the amount of core boundary mixing in any of the stars we consider. Instead, we report their core masses and compare our results to previous studies.
Conclusions. We find that the per-cent level precision on fundamental stellar quantities are accompanied with core mass estimates to a precision between ∼5% and 15%. We find that differences in analysis techniques can lead to substantially different evolutionary modelling results, which calls for the compilation of a homogeneously analysed sample to draw inferences on internal physical processes.
Key words: binaries: eclipsing / stars: fundamental parameters / stars: interiors / stars: evolution / stars: individual: CW Cep / stars: individual: U Oph
© ESO 2019
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