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Article Dans Une Revue Astronomy and Astrophysics - A&A Année : 2010

Absolute dimensions of solar-type eclipsing binaries. III. EW Orionis: stellar evolutionary models tested by a G0 V system

Résumé

Context. Recent studies of inactive and active solar-type binaries suggest that chromospheric activity, and its effect on envelope convection, is likely to cause significant radius and temperature discrepancies. Accurate mass, radius, and abundance determinations from additional solar-type binaries exhibiting various levels of activity are needed for a better insight into the structure and evolution of these stars.
Aims: We aim to determine absolute dimensions and abundances for the G0 V detached eclipsing binary EW Ori, and to perform a detailed comparison with results from recent stellar evolutionary models.
Methods: uvby light curves and {uvby}beta standard photometry were obtained with the Strömgren Automatic Telescope, published radial velocity observations from the CORAVEL spectrometer were reanalysed, and high-resolution spectra were observed at the FEROS spectrograph; all are/were ESO, La Silla facilities. State-of-the-art methods were applied for the photometric and spectroscopic analyses.
Results: Masses and radii that are precise to 0.9% and 0.5%, respectively, have been established for both components of EW Ori. The 1.12 M&sun; secondary component reveals weak Ca ii H and K emission and is probably mildly active; no signs of activity are seen for the 1.17 M&sun; primary. We derive an [Fe/H] abundance of +0.05 ± 0.09 and similar abundances for Si, Ca, Sc, Ti, Cr, and Ni. Yonsai-Yale and Granada solar-scaled evolutionary models for the observed metal abundance reproduce the components fairly well at an age of ≈2 Gyr. Perfect agreement is, however, obtained at an age of 2.3 Gyr for a combination of a) a slight downwards adjustment of the envelope mixing length parameter for the secondary, as seen for other active solar-type stars; and b) a slightly lower helium content than prescribed by the Y-Z relations adopted for the standard model grids. The orbit is eccentric (e = 0.0758 ± 0.0020), and apsidal motion with a 62% relativistic contribution has been detected. The apsidal motion period is U = 16 300 ± 3900 yr, and the inferred mean central density concentration coefficient, log(k2) = -1.66 ± 0.30, agrees marginally with model predictions. The measured rotational velocities, 9.0 ± 0.7 (primary) and 8.8 ± 0.6 (secondary) km s-1, are in agreement with both the synchronous velocities and the theoretically predicted pseudo-synchronous velocities. Finally, the distance (175 ± 7 pc), age, and center-of mass velocity (6 km s-1) exclude suggested membership of the open cluster Collinder 70.
Conclusions: EW Ori now belongs to the small group of solar-type eclipsing binaries with well-established astrophysical properties.

Dates et versions

hal-03730708 , version 1 (20-07-2022)

Identifiants

Citer

J. V. Clausen, H. Bruntt, E. H. Olsen, B. E. Helt, A. Claret. Absolute dimensions of solar-type eclipsing binaries. III. EW Orionis: stellar evolutionary models tested by a G0 V system. Astronomy and Astrophysics - A&A, 2010, 511, pp.22. ⟨10.1051/0004-6361/200913698⟩. ⟨hal-03730708⟩
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