The age of the Methuselah star in light of stellar evolution models with tailored abundances

TL;DR

This study refines the age of the Methuselah star HD140283 using tailored stellar evolution models with specific elemental abundances, highlighting the importance of detailed chemical composition in age determination.

Contribution

It introduces tailored stellar models incorporating recent spectroscopic data, demonstrating their impact on more accurate age estimates of HD140283 compared to generic models.

Findings

Age of HD140283 is approximately 12.3 billion years with tailored models.

Using solar-scaled abundances yields an age of about 14 billion years.

Elemental abundances significantly influence age estimates, comparable to effects of mixing length parameter adjustments.

Abstract

Context. HD140283, or the Methuselah star, is a well-known reference object in stellar evolution. Its peculiar chemical composition, proximity and absence of reddening makes it an interesting case-study of Pop II stars. Thanks to recent observational efforts, we now have precise interferometric and spectroscopic constraints, as well as revised astrometric parallaxes from the Gaia mission. Aims. We aim at determining the age of HD140283 with these lastest constraints, as well as quantifying the impact of systematics from physical inaccuracies in the stellar evolution models. Methods. Using recent spectroscopic abundances from the literature, including 3D non-LTE values for C, O, and Fe, we compute opacity tables specific to HD140283. We then use them in grids of stellar evolution models coupled to a Markov Chain Monte Carlo tool to determine the age of HD140283. Results. With our tailored models we find an age of 12.3Gy. Using a solar-scaled mixture instead results in an age value of 14Gy, in tension with the age of the universe ($13.77\pm0.06$Gy). We also find that reducing the mixing length parameter from its solar calibrated value will lead to an even lower age, in agreement with other recent studies. However, we find no direct evidence to favour a lower mixing length parameter value from our modelling. Conclusions. Taking into account the specific elemental abundances is crucial for the modelling of HD140283, as it leads to significant differences in the inferred age. However, this effect is degenerate with a lowering of the mixing length parameter. In this respect, asteroseismic constraints might play a key role in accurately deriving the mass of HD140283, therefore strongly constraining its age.