How precisely can we measure the ages of subgiant and giant stars?

TL;DR

The paper investigates how precisely we can measure ages for subgiant and giant stars by using wide binaries as an empirical, model-independent benchmark. It contrasts three age catalogs—XiangRix2022 (spectroscopic subgiants), Nataf2024 (photometric subgiants), and Wang2023 (giant RGB/RC ages derived from LAMOST with asteroseismic proxies)—against a Gaia DR3-based wide-binary sample extended to 5 kpc. Results show that subgiant ages with spectroscopic metallicities and $\alpha$-abundances (XR22) have realistic uncertainties (median $\sim$7.5%); giant ages (Wang2023) are reliable at $\sim$25–30%, while Nataf2024 underestimates uncertainties by factors of $\sim2$–$3$, likely due to systematics in photometric metallicity. The study demonstrates that accurate abundances are essential for precise subgiant ages and establishes wide binaries as a robust, model-independent benchmark for calibrating stellar age measurements in the era of large spectroscopic surveys, with complementary constraints from chemical clocks like [C/N] for red giants. As surveys grow, these benchmarks will be crucial for delivering reliable ages across the Galaxy.

Abstract

Precise stellar ages are fundamental to Galactic archaeology. However, obtaining reliable age estimates and uncertainties for field stars has been a long-standing challenge. We test the fidelity of ages from recent catalogs of giants and subgiants using wide binaries, whose components formed at the same time and thus should have consistent inferred ages. We find that subgiant ages based on spectroscopic metallicities from Xiang & Rix (2022) are generally consistent within their reported uncertainties, implying that fractional uncertainties of 5-10% are realistically achievable. In contrast, we find that published photometric subgiant ages underestimate true uncertainties by factors of 2-3. Spectroscopic age estimates for red giant and red clump stars also show reliable uncertainties, but are generally less precise (25-30%). These results demonstrate that accurate metallicity and $α$-element abundances are essential for precise subgiant ages and establish wide binaries as a powerful, model-independent benchmark for calibrating stellar age measurements in the era of large spectroscopic surveys.

Figures (1)

• Figure 1: Calibrating subgiant and giant star age uncertainties using wide binaries. Top: Kiel diagrams ($T_{\rm eff}$-$\log g$) for the stars in each sample: XiangRix2022 subgiants (purple; hollow points show the outlier), Nataf2024 subgiants (green, red outline for the Primary Sample), and Wang2023 LAMOST red giants (blue, red outline for SNR$>50$). The black points in the background show a randomly selected LAMOST sample with SNR$>50$ for reference. Bottom: wide binary component age comparisons. Dashed lines indicate $1:1$ correspondence, and the annotated $\sigma_z$ values denote the standard deviation of $z$ (Equation \ref{['eq:z']}), where $\sigma_z>1$ implies that true dispersions exceed quoted uncertainties. Subgiant ages based on spectroscopic metallicities show consistency with reported errors XiangRix2022, while subgiants with photometric metallicities and red giants display underestimation of age uncertainties by factors of $\sim2-5$.