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Register a new userEclipsing binaries in open clusters. III. V621 Per in chi Persei
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J. Southworth
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V621 Persei is a detached eclipsing binary in the open cluster chi Persei which is composed of an early B-type giant star and a main sequence secondary component. From high-resolution spectroscopic observations and radial velocities from the literature, we determine the orbital period to be 25.5 days and the primary velocity semiamplitude to be K = 64.5 +/- 0.4 km/s. No trace of the secondary star has been found in the spectrum. We solve the discovery light curves of this totally-eclipsing binary and find that the surface gravity of the secondary star is log(g_B) = 4.244 +/- 0.054 (cm/s). We compare the absolute masses and radii of the two stars in the mass--radius diagram, for different possible values of the primary surface gravity, to the predictions of stellar models. We find that log(g_A) is approximately 3.55, in agreement with values found from fitting Balmer lines with synthetic profiles. The expected masses of the two stars are 12 Msun and 6 Msun, and the expected radii are 10 Rsun and 3 Rsun. The primary component is near the blue loop stage in its evolution.
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The orbit and physical parameters of the previously unsolved SB2 EB V570 Per are derived using high resolution Asiago Echelle spectroscopy and B, V photo-electric photometry. The metallicity from chi^2 analysis is [M/H]=+0.02 +/- 0.03, and reddening from interstellar NaI and KI absorption lines is E(B-V) =0.023 +/- 0.007. The two components have masses of 1.449 +/- 0.006 and 1.350 +/- 0.006 Msun and spectral types F3 and F5, respectively. They are both still within the Main Sequence band (T_1 =6842 +/- 25 K, T_2 =6562 +/- 25 K from chi^2 analysis, R_1 =1.523 +/- 0.030, R_2 =1.388 +/- 0.019 Rsun) and are dynamically relaxed to co-rotation with the orbital motion (Vrot sin i_{1,2} =40 and 36 (+/-1) km/sec). The distance to V570 Per obtained from the orbital solution is 123 +/- 2 pc, in excellent agreement with the revised Hipparcos distance of 123 +/- 11 pc. The observed properties of V570 Per components are compared to BaSTI models computed on purpose for exactly the observed masses and varied chemical compositions. This system is interesting since both components have their masses in the range where the efficiency of convective core overshooting has to decrease with the total mass as a consequence of the decreasing size of the convective core during the central H-burning stage. Our numerical simulations show that, a small but not null overshooting is required, with efficiencies lambda_{OV} =0.14 and 0.11 for the 1.449 and 1.350 Msun components, respectively. This confirms the finding of Paper II on the similar system V505 Per. At the approx 0.8 Gyr age of the system, the element diffusion has reduced the surface metallicity of the models from the initial [M/H]=+0.17 to [M/H]=+0.02, in perfect agreement with the spectroscopically derived [M/H]=+0.02 +/- 0.03 value.
As a result of the variability survey in Chi Persei and NGC6910, the number of Beta Cep stars that are members of these two open clusters is increased to twenty stars, nine in NGC6910 and eleven in Chi Persei. We compare pulsational properties, in particular the frequency spectra, of Beta Cep stars in both clusters and explain the differences in terms of the global parameters of the clusters. We also indicate that the more complicated pattern of the variability among B type stars in Chi Persei is very likely caused by higher rotational velocities of stars in this cluster. We conclude that the sample of pulsating stars in the two open clusters constitutes a very good starting point for the ensemble asteroseismology of Beta Cep-type stars and maybe also for other B-type pulsators.
The orbit and fundamental physical parameters of the double-lined eclipsing binary V505 Per are derived by means of Echelle high resolution, high S/N spectroscopy and B, V photometry. Effective temperatures, gravities, rotational velocities and metallicities are obtained from atmospheric chi^2 analysis. An E(B-V)<=0.01 mag reddening is derived from interstellar NaI and KI lines. The distance to the system computed from orbital parameters (60.6 +/- 1 pc) is identical to the newly re-reduced Hipparcos parallax (61.5 +/- 1.9 pc). The masses of the two components (M(1) = 1.2693 +/- 0.0011 and M(2) = 1.2514 +/- 0.0012 Msun) place them in the transition region between convective and radiative stellar cores of the HR diagram, with the more massive of the two showing already the effect of evolution within the Main Sequence band (T(1) = 6512 +/- 21 K, T(2) = 6462 +/- 12 K, R(1) = 1.287 +/- 0.014, R(2) = 1.266 +/- 0.013 Rsun). This makes this system of particular relevance to theoretical stellar models, as a test on the overshooting. We compare the firm observational results for V505 Per component stars with the predictions of various libraries of theoretical stellar models (BaSTI, Padova, Granada, Yonsei-Yale, Victoria-Regina) as well as BaSTI models computed specifically for the masses and chemical abundances of V505 Per. We found that the overshooting at the masses of V505 Per component stars is already pretty low, but not null, and described by efficiencies lambda(OV)=0.093 and 0.087 for the 1.27 and 1.25 Msun components, respectively. According to the computed BaSTI models, the age of the system is about 0.9 Gyr and the element diffusion during this time has reduced the surface metallicity from the initial [M/H]=-0.03 to the current [M/H]=-0.13, in excellent agreement with observed [M/H]=-0.12 +/- 0.03.
The population statistics of binary stars are an important output of star formation models. However populations of wide binaries evolve over time due to interactions within a systems birth environment and the unfolding of wide, hierarchical triple systems. Hence the wide binary populations observed in star forming regions or OB associations may not accurately reflect the wide binary populations that will eventually reach the field. We use Gaia DR2 data to select members of three open clusters, Alpha~Per, the Pleiades and Praesepe and to flag cluster members that are likely unresolved binaries due to overluminosity or elevated astrometric noise. We then identify the resolved wide binary population in each cluster, separating it from coincident pairings of unrelated cluster members. We find that these clusters have an average wide binary fraction in the 300-3000,AU projected separation range of 2.1$pm^{0.4}_{0.2}$% increasing to 3.0$pm^{0.8}_{0.7}$% for primaries with masses in the 0.5-1.5,$M_{odot}$ range. This is significantly below the observed field wide binary fraction, but shows some wide binaries survive in these dynamically highly processed environments. We compare our results with another open cluster (the Hyades) and two populations of young stars that likely originated in looser associations (Young Moving Groups and the Pisces-Eridanus stream). We find that the Hyades also has a deficit of wide binaries while the products of looser associations have wide binary fractions at or above field level.
V505 Per is a detached eclipsing binary containing two F5 V stars in a 4.22-d circular orbit. We use a light curve from the TESS satellite and published radial velocity measurements to establish the properties of the system to high precision. The masses of the stars are 1.275 +/- 0.004 Msun and 1.258 +/- 0.003 Msun, and their radii are 1.294 +/- 0.002 Rsun and 1.264 +/- 0.002 Rsun. Adding published effective temperature estimates, we precisely measure the luminosities and absolute bolometric magnitudes of the stars, and the distance to the system. The distance is slightly shorter than that obtained from the Gaia EDR3 parallax, a discrepancy most easily explained by uncertainty in the 2MASS K-band apparent magnitude. We reanalyse existing light and radial velocity curves from three previous studies of this system and conclude that, in this case, formal errors are reliable for the spectroscopic orbits but not light curves, that errorbars from a residual-permutation algorithm are suitable for light curves but not spectroscopic orbits, and that published results are not always reproducible. The precisions in the measured properties of V505 Per are high and among the best ever obtained for a detached eclipsing binary system.
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