TY - JOUR
T1 - Absolute dimensions of eclipsing binaries XXVIII. BK pegasi and other F-type binaries
T2 - prospects for calibration of convective core overshoot
AU - Clausen, Jens Viggo
AU - Frandsen, S.
AU - Bruntt, H.
AU - Olsen, E. H.
AU - Helt, B. E.
AU - Gregersen, Kristian Anders
AU - Juncher, D.
AU - Krogstrup, Peter
PY - 2010/6
Y1 - 2010/6
N2 - 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 ⊙ terval 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 5d.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 ⊙}, 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 ⊙ 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 ⊙ eclipsing binaries to fine-tune convective core overshoot, diffusion, and possibly other ingredients of modern theoretical evolutionary models.
AB - 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 ⊙ terval 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 5d.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 ⊙}, 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 ⊙ 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 ⊙ eclipsing binaries to fine-tune convective core overshoot, diffusion, and possibly other ingredients of modern theoretical evolutionary models.
U2 - 10.1051/0004-6361/201014266
DO - 10.1051/0004-6361/201014266
M3 - Journal article
SN - 0004-6361
VL - 516
SP - A42
JO - Astronomy & Astrophysics
JF - Astronomy & Astrophysics
ER -