Is [Y/Mg] a Reliable Age Diagnostic for FGK Stars?

TL;DR

This study evaluates the [Y/Mg] ratio as an age indicator for FGK stars, finding it most precise for solar twins but also useful across a broader stellar range, with systematic uncertainties considered.

Contribution

It demonstrates the applicability and limitations of the [Y/Mg] ratio as an age diagnostic for diverse FGK stars, extending previous findings beyond solar twins.

Findings

[Y/Mg] is most precise for solar twins with a slope of -0.0370 dex/Gyr.

A systematic uncertainty of 1.5 Gyr is recommended for age estimates using [Y/Mg].

The [Y/Mg] Clock shows potential as an age indicator for FGK stars beyond solar twins.

Abstract

Current spectroscopic surveys are producing large catalogs of chemical abundances for stars of all types. The yttrium to magnesium ratio, [Y/Mg], has emerged as a candidate age indicator for solar twins in the local stellar neighborhood. However, it is unclear whether it is a viable age diagnostic for more diverse stellar types, so we investigate [Y/Mg] as an age indicator for the FGK-type planet host stars observed by $Kepler$. We find that the [Y/Mg] "Clock" is most precise for solar twins, with a [Y/Mg]/Age slope of $m$ = $-$0.0370 $\pm$ 0.0071 dex/Gyr and $\sigma_{\mathrm{Age}}$ = 2.6 Gyr. We attribute the lower precision compared to literature results to non-solar twins contaminating our solar twin sample and recommend a 1.5 Gyr systematic uncertainty for stellar ages derived with any [Y/Mg]-Age relation. We also analyzed the [Y/Mg] Clock as a function of $T_{\mathrm{eff}}$, $\log g$, and metallicity individually and find no strong trends, but compute statistically significant [Y/Mg]-Age relations for subsamples defined by ranges in $T_{\mathrm{eff}}$, $\log g$, and metallicity. Finally, we compare [Y/Mg] and rotation ages and find statistically similar trends as for isochrone ages, although we find that rotation ages perform better for GK dwarfs while isochrones perform better for FG subgiants. We conclude that the [Y/Mg] Clock is most precise for solar twins and analogs but is also a useful age diagnostic for FGK stars.