Advancing the accuracy in age determinations of old-disk stars using an oscillating red giant in an eclipsing binary

¹ Dipartimento di Fisica e Astronomia, Università di Bologna, Via Zamboni 33, Bologna 40126, Italy
² Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, INAF, Via Gobetti 93/3, Bologna 40129, Italy
³ Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, Aarhus C 8000, Denmark
⁴ School of Physics and Astronomy, University of Birmingham, B15 2TT Birmingham, United Kingdom
⁵ Osservatorio Astronomico di Padova, INAF, Vicolo dell’Osservatorio 5, Padova 35122, Italy
⁶ Research School of Astronomy & Astrophysics, Australian National University, Cotter Rd., Weston, ACT 2611, Australia
⁷ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Stromlo, Australia
⁸ Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife, Spain
⁹ Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Spain
¹⁰ Nordic Optical Telescope, Rambla José Ana Fernández Pérez 7, Breña Baja, La Palma 38711, Spain
¹¹ Institut d’Astrophysique et Géophysique, l’Université de Liège, Allée du 6 août 17, Liège 4000, Belgium
¹² LIRA, Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris Cité, CY Cergy Paris Université, CNRS, 92190 Meudon, France
¹³ Astrophysics Group, Keele University, Staffordshire, ST5 5BG Newcastle-under-Lyme, United Kingdom
¹⁴ Department of Physics and Astronomy, University of Turku, Turku 20014, Finland
¹⁵ Department of Physics, P.O. Box 64 FI-00014 University of Helsinki, Helsinki, Finland
¹⁶ Armagh Observatory and Planetarium, College Hill, BT61 9DG Northern Ireland, UK
¹⁷ University of Craiova, Alexandru Ioan Cuza 13, Craiova 200585, Romania
¹⁸ CAHA, Observatorio de Calar Alto, Sierra de los Filabres, Gérgal 04550, Spain
¹⁹ GRANTECAN, Cuesta de San José s/n, E-38712 Breña Baja, La Palma, Spain
²⁰ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Santiago, Chile

^⋆ Corresponding author: j.s.thomsen@pm.me

Received: 8 December 2024
Accepted: 23 April 2025

Abstract

Context. The study of resonant oscillation modes in low-mass red giant branch stars enables us to infer their ages with exceptional (∼10%) precision. This unlocks the possibility to reconstruct the temporal evolution of the Milky Way at early cosmic times. Ensuring the accuracy of such a precise age scale is a fundamental but difficult challenge. Because the age of red giant branch stars primarily hinges on their mass, an independent mass determination for an oscillating red giant star provides the means for this assessment.

Aims. We analysed the old eclipsing binary KIC 10001167, which hosts an oscillating red giant branch star and is a member of the thick disk of the Milky Way. Of the known red giants in eclipsing binaries, this is the only member of the thick disk whose asteroseismic signal is of a high enough quality to test the seismic mass inference at the 2% level.

Methods. We measured the binary orbit and obtain fundamental stellar parameters through a combined analysis of light-curve eclipses and radial velocities, and we performed a detailed asteroseismic, photospheric, and Galactic kinematic characterisation of the red giant and the binary system.

Results. We show that the dynamically determined mass 0.9337 ± 0.0077 M_⊙ (0.8%) of this 10 Gyr old star agrees within 1.4% with the mass inferred from a detailed modelling of individual pulsation mode frequencies (1.6%). This is now the only thick-disk stellar system that hosts a red giant for which the mass has been determined asteroseismically with a precision better than 2% and through a model-independent method at a precision of 1%. We hereby affirm the potential of asteroseismology to define an accurate age scale for ancient stars to trace the Milky Way assembly history.