HD 71636, A Newly Discovered Eclipsing Binary

Henry, Gregory W.; Fekel, Francis C.; Sowell, James R.; Gearhart, Joel S.

doi:10.1086/508684

Cited by 14 publications

(26 citation statements)

References 29 publications

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“…We believe, however, that this is due to problems with the published radii. A re-analysis of the light curves by Henry et al (2006) indicates that the ratio between the (relative) radii is significantly more uncertain than given by the authors 11 , most probably because the secondary eclipse is far from being well-covered.…”

Section: Comparison With Other Binariesmentioning

confidence: 77%

Absolute dimensions of eclipsing binaries

Clausen¹,

Frandsen

Bruntt

et al. 2010

A&A

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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.

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Section: Comparison With Other Binariesmentioning

confidence: 77%

Absolute dimensions of eclipsing binaries

Clausen¹,

Frandsen

Bruntt

et al. 2010

A&A

View full text Add to dashboard Cite

show abstract

“…The latter is often determined from the result of the solar calibration (Y ⊙ − Y P )/Z ⊙ and for any other star of known metallicity, the helium abundance is scaled to the solar one as . Most of the conclusions drawn when comparing theoretical isochrones with binaries (Torres et al 2002, 2006; Torres & Ribas 2002; Lacy et al 2005; Boden, Torres & Latham 2006; Henry et al 2006) and field stars (e.g. Allende Prieto & Lambert 1999; Valenti & Fischer 2005) thus reflect this tacit assumption on the helium content.…”

Section: Introductionmentioning

confidence: 99%

“…Most of the conclusions drawn when comparing theoretical isochrones with binaries (e.g. Torres & Ribas 2002;Lacy et al 2005;Torres et al 2006;Boden, Torres & Latham 2006;Henry et al 2006) and field stars (e.g. thus reflect this tacit assumption on the helium content.…”

Section: Introductionmentioning

confidence: 99%

The helium abundance and ΔY/ΔZ in lower main-sequence stars

Casagrande

Flynn

Portinari

et al. 2007

Monthly Notices of the Royal Astronomical Society

116

136

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We use nearby K dwarf stars to measure the helium-to-metal enrichment ratio Y/ Z, a diagnostic of the chemical history of the solar neighbourhood. Our sample of K dwarfs has homogeneously determined effective temperatures, bolometric luminosities and metallicities, allowing us to fit each star to the appropriate stellar isochrone and determine its helium content indirectly. We use a newly computed set of Padova isochrones which cover a wide range of helium and metal content.Our theoretical isochrones have been checked against a congruous set of main-sequence binaries with accurately measured masses, to discuss and validate their range of applicability. We find that the stellar masses deduced from the isochrones are usually in excellent agreement with empirical measurements. Good agreement is also found with empirical mass-luminosity relations.Despite fitting the masses of the stars very well, we find that anomalously low helium content (lower than primordial helium) is required to fit the luminosities and temperatures of the metalpoor K dwarfs, while more conventional values of the helium content are derived for the stars around solar metallicity.We have investigated the effect of diffusion in stellar models and the assumption of local thermodynamic equilibrium (LTE) in deriving metallicities. Neither of these is able to resolve the low-helium problem alone and only marginally if the cumulated effects are included, unless we assume a mixing-length which is strongly decreasing with metallicity. Further work in stellar models is urgently needed.The helium-to-metal enrichment ratio is found to be Y/ Z = 2.1 ± 0.9 around and above solar metallicity, consistent with previous studies, whereas open problems still remain at the lowest metallicities. Finally, we determine the helium content for a set of planetary host stars.

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Section: Comparison With Other Binariesmentioning

confidence: 81%

Absolute dimensions of eclipsing binaries. XXVIII. BK Pegasi and other F-type binaries: Prospects for calibration of convective core overshoot

Clausen,

Frandsen,

Bruntt

et al. 2010

Preprint

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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. Yonsei-Yale 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.

show abstract

HD 71636, A Newly Discovered Eclipsing Binary

Cited by 14 publications

References 29 publications

Absolute dimensions of eclipsing binaries

Absolute dimensions of eclipsing binaries

The helium abundance and ΔY/ΔZ in lower main-sequence stars

Absolute dimensions of eclipsing binaries. XXVIII. BK Pegasi and other F-type binaries: Prospects for calibration of convective core overshoot

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