Properties of the Hyades, the eclipsing binary HD 27130, and the oscillating red giant ϵ Tauri

Abstract

Context. The derivation of accurate and precise masses and radii is possible for eclipsing binary stars, allowing for insights into their evolution. When residing in star clusters, they provide measurements of even greater precision, along with additional information on their properties. Asteroseismic investigations of solar-like oscillations offers similar possibilities for single stars. Aims. We wish to improve the previously established properties of the Hyades eclipsing binary HD 27130 and re-assess the asteroseismic properties of the giant star ϵ Tau. The physical properties of these members of the Hyades can be used to constrain the helium content and age of the cluster. Methods. New multi-colour light curves were combined with multi-epoch radial velocities to yield masses and radii of HD 27130. Measurements of Teff were derived from spectroscopy and photometry, and verified using the Gaia parallax. We estimated the cluster age from re-evaluated asteroseismic properties of ϵ Tau while using HD 27130 to constrain the helium content. Results. The masses, radii, and Teff of HD 27130 were found to be M = 1.0245  ±  0.0024 M⊙, R = 0.9226  ±  0.015 R⊙, Teff = 5650  ±  50 K for the primary, and M = 0.7426  ±  0.0016 M⊙, R = 0.7388  ±  0.026 R⊙, Teff = 4300  ±  100 K for the secondary component. Our re-evaluation of ϵ Tau suggests that the previous literature estimates are trustworthy and that the HIPPARCOS parallax is more reliable than the Gaia DR2 parallax. Conclusions. The helium content of HD 27130 and, thus, of the Hyades is found to be Y = 0.27 but with a significant model dependency. Correlations with the adopted metallicity result in a robust helium enrichment law, with ΔY/ΔZ close to 1.2 We estimate the age of the Hyades to be 0.9 ± 0.1 (stat) ±0.1 (sys) Gyr, which is in slight tension with recent age estimates based on the cluster white dwarfs. The precision of the age estimate can be much improved via asteroseismic investigations of the other Hyades giants and by future improvements to the Gaia parallax for bright stars.