Calibration of the [C/N] and [Y/Mg] chemical clocks with asteroseismic ages from the TESS space mission

TL;DR

This study calibrates chemical clocks [C/N] and [Y/Mg] with asteroseismic ages from TESS data, revealing their dependence on Galactic location and stellar evolution, and emphasizing the importance of NLTE abundances.

Contribution

It provides new empirical relations between chemical abundance ratios and stellar ages, accounting for Galactic and evolutionary effects, using TESS asteroseismic data.

Findings

[Y/Mg]-age relation varies across the Galactic disc

NLTE abundances improve age estimates from [Y/Mg]

Evolutionary stages must be considered when using [C/N] as an age indicator

Abstract

Context. Stellar ages are typically very difficult to estimate for field stars. New empirical methods, based on abundance ratios of chemical elements, are emerging and need to be calibrated. Aims. Our main aim is to contribute to revealing relations between [C/N] and [Y/Mg] ratios and stellar ages by determining astroseismic ages and non-local thermodynamic equilibrium (NLTE) abundances, and accounting for stellar evolutionary stages and birth places in the Galaxy. Methods. We searched for solar pulsations in a sample of 1250 bright F, G, and K giants using data from the TESS space telescope and determined asteroseismic ages using the BASTA and PARAM codes. For the [Y/Mg] relations with age, we determined abundances accounting for deviations from the local thermodynamic equilibrium. For the [C/N] relations with age, we separated stars according to their evolutionary stages. Results. We determined asteroseismic ages for 218 giants and derived [Y/Mg] and [C/N] relations with age for subsamples of stars in three regions of the Galactic thin disc and the thick disc. Conclusions. The [Y/Mg]-age relation exhibits a clear radial dependence across the Galactic disc, with a steeper trend in the outer disc, progressively flatter relations towards the inner disc, and a very flat trend in the thick disc. NLTE abundances of Mg and especially of Y have to be used in order to obtain a more precise stellar age evaluation from [Y/Mg] ratios. When using [C/N] abundance ratios as stellar age indicators, evolutionary stages of stars have to be taken into account.