The GALAH survey: tracing the Galactic disk with Open Clusters

TL;DR

This study uses Gaia and spectroscopic data from GALAH and APOGEE to analyze open clusters, revealing their chemical distribution and gradients in the Galactic disk, and comparing them to field stars to understand Galactic chemical evolution.

Contribution

It provides a comprehensive chemical and spatial analysis of open clusters in the Galactic disk, highlighting differences from field stars and implications for Galactic evolution models.

Findings

Radial metallicity gradient of -0.076 dex/kpc consistent with previous studies.

Open clusters show less scatter in age-metallicity relation than field stars.

Identifies trends in element ratios with guiding radius and age.

Abstract

Open clusters are unique tracers of the history of our own Galaxy's disk. According to our membership analysis based on \textit{Gaia} astrometry, out of the 226 potential clusters falling in the footprint of GALAH or APOGEE, we find that 205 have secure members that were observed by at least one of the survey. Furthermore, members of 134 clusters have high-quality spectroscopic data that we use to determine their chemical composition. We leverage this information to study the chemical distribution throughout the Galactic disk of 21 elements, from C to Eu. The radial metallicity gradient obtained from our analysis is $-$0.076$\pm$0.009 dex kpc$^{-1}$, which is in agreement with previous works based on smaller samples. Furthermore, the gradient in the [Fe/H] - guiding radius (r$_{\rm guid}$) plane is $-$0.073$\pm$0.008 dex kpc$^{-1}$. We show consistently that open clusters trace the distribution of chemical elements throughout the Galactic disk differently than field stars. In particular, at given radius, open clusters show an age-metallicity relation that has less scatter than field stars. As such scatter is often interpreted as an effect of radial migration, we suggest that these differences are due to the physical selection effect imposed by our Galaxy: clusters that would have migrated significantly also had higher chances to get destroyed. Finally, our results reveal trends in the [X/Fe]$-$r$_{\rm guid}$$-$age space, which are important to understand production rates of different elements as a function of space and time.