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Register a new userRediscussion of eclipsing binaries. Paper VI. The F-type system V505 Persei
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John Southworth
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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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V455 Aur is a detached eclipsing binary containing two F-stars in a 3.15-d orbit with a small eccentricity. Its eclipses were discovered in data from the Hipparcos satellite and a spectroscopic orbit was obtained by Griffin (2001, 2013). Griffin found a long-term variation of the systemic velocity of the eclipsing system due to a third body in a highly eccentric orbit (e = 0.73) with a period of 4200 d. We have used these data, the light curve of V455 Aur from the TESS satellite, and the Gaia EDR3 parallax to determine the physical properties of the components of the system to high precision. We find the eclipsing stars to have masses of 1.289 +/- 0.006 Msun and 1.232 +/- 0.005 Msun, radii of 1.389 +/- 0.011 Rsun and 1.318 +/- 0.014 Rsun and effective temperatures of 6500 +/- 200 and 6400 +/- 200 K. Light from the tertiary component is directly detected for the first time, in the form of a third light of l_3 = 0.028 +/- 0.002 in the solution of the TESS light curve. From this l_3, theoretical spectra and empirical calibrations we estimate the star to have a mass of 0.72 +/- 0.05 Msun, a radius of 0.74 +/- 0.05 Rsun and a temperature of 4300 +/- 300 K. The inclination of the outer orbit is 53 +/- 3 degrees, so the two orbits in the system are not coplanar. We show that a measured spectroscopic light ratio of the two eclipsing stars could lower the uncertainties in radius from 1% to 0.25%. A detailed spectroscopic analysis could also yield precise temperatures and chemical abundances of the system, thus making V455 Aur one of the most precisely measured eclipsing systems known.
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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.
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