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

I led an international team in this high-precision study of the only old red giant hosting eclipsing binary with high enough asteroseismic data quality to validate the stellar mass against eclipsing binary analysis at the 1.4% level. We managed to obtain a 6% agreement on the age, and thereby affirm the use of precise asteroseismology for Galactic Archaeology.

This is a completely unique cosmic test, since we have measured the mass of an ancient star with two entirely different methods, one of them dependent only on the mutual gravitational attraction with its companion star. The 1.4% agreement remarks a milestone in our ability to characterize old stars and use them as living fossils to study the Milky Way’s distant past.

Illustration of the eclipsing binary KIC10001167 with an up-close view of the orbit from our perspective (bottom left) and as seen from above (top right). The curves demonstrate what we can observe from earth, the amount of light coming from the system (top left) as well as the velocity of the two stars towards/away from us (bottom right).

Here you can find an illustration of the red giant star’s oscillations.

The study comprised researchers from Bologna (IT), Aarhus (DK), Padova (IT), Australia, La Palma (ES), Liege (BE), Paris (FR), Keele (UK), and ESO (CL).

After publication in Astronomy & Astrophysics, this article was featured at several of the collaborating institutes, as well as in the Italian and Canarian media: ANSA (Italian), Astronomy & Astrophysics, University of Bologna (Italian), University of Bologna (English), Nordic Optical Telescope, Aarhus University (Danish), Aarhus University (English), Keele University, Instituto Astrofisica Canarias.

Paper 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.