Absolute dimensions of solar-type eclipsing binaries.

et al. 2008

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Context. Accurate mass, radius, and abundance determinations from binaries provide important information on stellar evolution, fundamental to central fields in modern astrophysics and cosmology. Aims. We aim to determine absolute dimensions and abundances for the three F-type main-sequence detached eclipsing binaries AD Boo, VZ Hya, and WZ Oph 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 at ESO, La Silla, radial velocity observations at CfA facilities, and supplementary high-resolution spectra with ESO's FEROS spectrograph. State-ofthe-art methods were applied for the analyses: the EBOP and Wilson-Devinney binary models, two-dimensional cross-correlation and disentangling, and the VWA abundance analysis tool. Results. Masses and radii that are precise to 0.5-0.7% and 0.4-0.9%, respectively, have been established for the components, which span the ranges of 1.1 to 1.4 M and 1.1 to 1.6 R . The [Fe/H] abundances are from -0.27 to +0.10, with uncertainties between 0.07 and 0.15 dex. We find indications of a slight α-element overabundance of [α/Fe] ∼ +0.1 for WZ Oph. The secondary component of AD Boo and both components of WZ Oph appear to be slightly active. Yale-Yonsai and Victoria-Regina evolutionary models fit the components of AD Boo and VZ Hya almost equally well, assuming coeval formation, at ages of about 1.75/1.50 Gyr (AD Boo) and 1.25/1.00 Gyr (VZ Hya). BaSTI models, however, predict somewhat different ages for the primary and secondary components. For WZ Oph, the models from all three grids are significantly hotter than observed. A low He content, decreased envelope convection coupled with surface activity, and/or higher interstellar absorption would remove the discrepancy, but its cause has not been definitively identified. Conclusions. We have demonstrated the power of testing and comparing recent stellar evolutionary models using eclipsing binaries, provided their abundances are known. The strongest limitations and challenges are set by T eff and interstellar absorption determinations, and by their effects on and correlation with abundance results.

Section: Discussionmentioning

confidence: 99%

Absolute dimensions of eclipsing binaries. XXVI.

Clausen¹,

Torres

et al. 2008

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“…Below, we present the new photometric material for BK Peg and refer to Clausen et al (2001;hereafter CHO01) for further details on observation and reduction procedures, and determination of times of minima.…”

Section: Photometrymentioning

confidence: 99%

Absolute dimensions of eclipsing binaries

Clausen¹,

Frandsen

et al. 2010

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Context. Double-lined, detached eclipsing binaries are our main source for accurate stellar masses and radii. In this paper we focus on the 1.15-1.70 M interval where convective core overshoot is gradually ramped up in theoretical evolutionary models. Aims. We aim to determine absolute dimensions and abundances for the F-type detached eclipsing binary BK Peg, and to perform a detailed comparison with results from recent stellar evolutionary models, including a sample of previously studied systems with accurate parameters. Methods. uvby light curves and uvbyβ standard photometry were obtained with the Strömgren Automatic Telescope, ESO, La Silla, and high-resolution spectra were acquired with the FIES spectrograph at the Nordic Optical Telescope, La Palma. Results. The 5. d 49 period orbit of BK Peg is slightly eccentric (e = 0.053). The two components are quite different with masses and radii of (1.414±0.007 M , 1.988±0.008 R ) and (1.257±0.005 M , 1.474±0.017 R ), respectively. The measured rotational velocities are 16.6 ± 0.2 (primary) and 13.4 ± 0.2 (secondary) km s −1 . For the secondary component this corresponds to (pseudo)synchronous rotation, whereas the primary component seems to rotate at a slightly lower rate. We derive an iron abundance of [Fe/H] = −0.12 ± 0.07 and similar abundances for Si, Ca, Sc, Ti, Cr and Ni. The stars have evolved to the upper half of the main-sequence band. YonseiYale and Victoria-Regina evolutionary models for the observed metal abundance reproduce BK Peg at ages of 2.75 and 2.50 Gyr, respectively, but tend to predict a lower age for the more massive primary component than for the secondary. We find the same age trend for three other upper main-sequence systems in a sample of well studied eclipsing binaries with components in the 1.15-1.70 M range. We also find that the Yonsei-Yale models systematically predict higher ages than the Victoria-Regina models. The sample includes BW Aqr, and as a supplement we have determined a [Fe/H] abundance of −0.07 ± 0.11 for this late F-type binary. Conclusions. We propose to use BK Peg, BW Aqr, and other well-studied 1.15-1.70 M eclipsing binaries to fine-tune convective core overshoot, diffusion, and possibly other ingredients of modern theoretical evolutionary models.

“…Below, we present the new photometric material for EW Ori and refer to Clausen et al (2001;hereafter CHO01) for further details on observation and reduction procedures, and determination of times of minima.…”

Section: Photometrymentioning

confidence: 99%

Absolute dimensions of solar-type eclipsing binaries

Clausen¹,

Olsen³

et al. 2010

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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 EW Ori. 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(k 2 ) = −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.