The [Y/Mg] chemical clock in the Galactic Disk: The influence of metallicity and Galactic population in the solar neighbourhood (2407.07283v2)

Abstract: Stellar ages are an important parameter to study the chemical evolution of the Galaxy. In recent years, several studies have established the existence of a relationship between chemical clocks and stellar ages. The [Y/Mg] clock is a promising technique, but there are still several open questions, such as its validity for metal-poor stars and differences between the thin and thick disk populations. Our aim is to study the behaviour of the [Y/Mg] chemical clock with stellar ages and the effect of metallicity and population on this chemical clock for a sample of solar-type disk stars. We have derived the precise stellar atmospheric parameters as well as the elemental abundances of Mg and Y through line-by-line differential spectroscopic analysis for a sample of 48 metal-poor solar-type stars based on high-quality, high-resolution ESO/HARPS spectra. From the high-precision Gaia astrometric data, stellar masses and ages were estimated through isochrone-fitting. A joint analysis of our sample, together with a sample of 185 solar-twins and analogues from our previous works, is performed to calibrate the [Y/Mg] chemical clock in the Galactic disk for $-$0.71 $\leq$ [Fe/H] $<$ +0.34. Open clusters and stars with asteroseismic ages have been used to validate our relations. Two different populations could be clearly seen in the [Mg/Fe] - [Fe/H] plane - the thick and thin disks. We found a metallicity-dependent, strong anti-correlation between the [Y/Mg] ratio and stellar ages of our sample. For the first time in the literature, we report similar correlations for the thin and thick disk stars. The [Y/Mg] relation(s) found here for solar-type stars is compatible with the literature using solar-twins. Our relation provides higher accuracy and precision of 0.45 and 0.99 Gyr, respectively, comparable with the best accuracy achieved for the solar-twins till date.

• The paper demonstrates the [Y/Mg] chemical clock’s effectiveness in estimating stellar ages via a metallicity-dependent anti-correlation for both thin and thick disk stars.
• It employs high-resolution spectroscopy and precise Gaia astrometry to derive stellar parameters and elemental abundances with exceptional accuracy.
• The findings challenge existing Galactic models by uncovering distinct age-metallicity relationships, prompting a re-evaluation of chemical evolution theories.

An Analysis of the [Y/Mg] Chemical Clock in the Galactic Disk

The paper "The [Y/Mg] chemical clock in the Galactic disk" provides a comprehensive investigation into the use of the [Y/Mg] chemical clock to estimate stellar ages within the Galactic disk. This paper aims to address several longstanding questions in Galactic archaeology, including the applicability of the chemical clock across different metallicity ranges and Galactic populations (thin and thick disks).

The research employs high-resolution, high-quality spectroscopic data obtained from the ESO/HARPS spectrograph, targeting 48 metal-poor solar-type stars. This dataset is further augmented by 185 solar twins and analogues from previous studies by the authors, resulting in a significant sample size for analysis. Stellar parameters, including effective temperature, surface gravity, and elemental abundances of Yttrium (Y) and Magnesium (Mg), are meticulously derived through differential spectroscopic analysis. Stellar ages and masses are calculated using precise Gaia astrometric data and the Yonsei-Yale isochrones, a robust isochrone fitting method.

Significantly, the paper highlights the presence of two distinct populations in the [Mg/Fe]-[Fe/H] plane, corresponding to the thin and thick disk stars. The thick disk stars exhibit an age-metallicity relationship, while the thin disk stars do not show a strong age-metallicity correlation, as evidenced by a flatter distribution. Importantly, the paper identifies a strong, metallicity-dependent anti-correlation between the [Y/Mg] ratio and stellar ages across the entire sample range ($-$0.71 ≤ [Fe/H] < +0.34). This work reports for the first time in literature that both thin and thick disk stars exhibit such correlations, thereby challenging previous assertions that the [Y/Mg] chemical clock is only applicable to thin disk stars.

Quantitatively, the paper presents equations that detail these relations, with particular emphasis on the strong anti-correlation for thin and thick disk stars. For the [Y/Mg] ratio, the research reports high accuracy and precision in age determination (0.45 and 0.99 Gyr, respectively), comparable to the best results achieved in solar twins to date.

The implications of these findings are twofold. Practically, they confirm the viability of the [Y/Mg] chemical clock for dating a broader category of stars within the Milky Way, offering a powerful tool for Galactic archaeology. Theoretically, the results suggest the need to revisit models of Galactic chemical evolution, particularly in regard to nucleosynthesis pathways and stellar populations in the Milky Way.

This research sets the groundwork for future studies aimed at enhancing our understanding of the Galactic disk's evolutionary history. It also prompts further investigation into the refinement of chemical clocks and highlights the potential interplay of Galactic dynamics with stellar nucleosynthesis processes. Future developments in AI and machine learning could potentially be leveraged to refine chemical abundance models further and automate the classification and characterization of stellar populations with unprecedented precision.