TY - JOUR
T1 - Absolute dimensions of solar-type eclipsing binaries III. EW orionis
T2 - stellar evolutionary models tested by a G0 V system
AU - Clausen, Jens Viggo
AU - Bruntt, H.
AU - Olsen, E. H.
AU - Helt, B. E.
AU - Claret, A.
PY - 2010/2/23
Y1 - 2010/2/23
N2 - 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 uvbyβ 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 EWOri. The 1.12 M⊙ 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⊙ 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: EWOri now belongs to the small group of solar-type eclipsing binaries with well-established astrophysical properties.
AB - 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 uvbyβ 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 EWOri. The 1.12 M⊙ 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⊙ 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: EWOri now belongs to the small group of solar-type eclipsing binaries with well-established astrophysical properties.
U2 - 10.1051/0004-6361/200913698
DO - 10.1051/0004-6361/200913698
M3 - Journal article
SN - 0004-6361
VL - 511
SP - A22
JO - Astronomy and Astrophysics Supplement Series
JF - Astronomy and Astrophysics Supplement Series
ER -