The [Y/Mg] clock works for evolved solar metallicity stars

TL;DR

This study confirms that the [Y/Mg] abundance ratio can serve as an effective age indicator for helium-core-burning stars of solar metallicity, extending its applicability beyond solar twins to evolved giants.

Contribution

It demonstrates that the [Y/Mg] clock is valid for evolved helium-core-burning stars, enabling broader age estimations across different stellar populations.

Findings

[Y/Mg] correlates with age in helium-core-burning stars.

The [Y/Mg] clock works for giant stars, not just solar twins.

Age estimates are more precise using asteroseismology and binary data.

Abstract

Previously [Y/Mg] has been proven to be an age indicator for solar twins. Here, we investigate if this relation also holds for helium-core-burning stars of solar metallicity. High resolution and high signal-to-noise ratio (S/N) spectroscopic data of stars in the helium-core-burning phase have been obtained with the FIES spectrograph on the NOT 2.56m telescope and the HIRES spectrograph on the Keck I 10 m telescope. They have been analyzed to determine the chemical abundances of four open clusters with close to solar metallicity; NGC 6811, NGC 6819, M67 and NGC 188. The abundances are derived from equivalent widths of spectral lines using ATLAS9 model atmospheres with parameters determined from the excitation and ionization balance of Fe lines. Results from asteroseismology and binary studies were used as priors on the atmospheric parameters, where especially the $\log g$ is determined to much higher precision than what is possible with spectroscopy. It is confirmed that the four open clusters are close to solar metallicity and they follow the [Y/Mg] vs. age trend previously found for solar twins. The [Y/Mg] vs. age clock also works for giant stars in the helium-core burning phase, which vastly increases the possibilities to estimate the age of stars not only in the solar neighborhood, but in large parts of the Galaxy, due to the brighter nature of evolved stars compared to dwarfs.