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

¹ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
e-mail: kfb@phys.au.dk
² Astronomical Observatory, Institute of Theoretical Physics and Astronomy, Vilnius University, Saulėtekio av. 3, 10257 Vilnius, Lithuania
³ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
⁴ Institut de Recherche sur les Exoplanètes, Département de Physique, Université de Montréal, Montréal, QC H3C 3J7, Canada
⁵ Department of Physics and Astronomy, University of Victoria, Victoria, BC V8W 2Y2, Canada
⁶ School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK
⁷ Astronomical Observatory, Department of Physical Sciences, Earth and Environment – University of Siena, Via Roma 56, 53100 Siena, Italy
⁸ Instituto de Astrofsica de Canarias, 38200 La Laguna, Tenerife, Spain
⁹ Universidad de La Laguna (ULL), Departamento de Astrofsica, 38206 La Laguna, Tenerife, Spain
¹⁰ Leiden Observatory, Leiden University, Postbus 9513 2300 RA Leiden, The Netherlands
¹¹ NOVA Optical IR Instrumentation Group at ASTRON, PO Box 2, 7990 AA Dwingeloo, The Netherlands
¹² Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
¹³ Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006, Australia

Received: 25 August 2020
Accepted: 2 November 2020

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 T_eff 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 T_eff of HD 27130 were found to be M = 1.0245  ±  0.0024 M_⊙, R = 0.9226  ±  0.015 R_⊙, T_eff = 5650  ±  50 K for the primary, and M = 0.7426  ±  0.0016 M_⊙, R = 0.7388  ±  0.026 R_⊙, T_eff = 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.