Stellar properties and chemical features of the Gaia Catalogue of Nearby Stars observed by GALAH DR4

TL;DR

The paper tackles the chemo-dynamical characterization of the solar neighborhood by combining Gaia GCNS astrometry with GALAH DR4 spectroscopic abundances for ~6,000 cross-matched stars. It uses PARSEC+COLIBRI isochrone ages and Galpy-based orbital parameters to classify Galactic components (thin/thick disc, halo) and to analyze chemical signatures such as $[Fe/H]$ and $[Mg/Fe]$. The results show a disc-dominated population with a median age around $1.6~\mathrm{Gyr}$ and $[Fe/H] \approx -0.19$ dex, plus a small halo fraction, laying groundwork for a detailed chemo-dynamical census. The work sets the stage for deeper exploitation of full spectroscopic data and orbital information from value-added catalogs to refine Galactic component classifications and the chemo-dynamical history of the solar neighborhood.

Abstract

The Gaia Catalogue of Nearby Stars (GCNS) comprises approximately 330 000 stars within 100 pc of the Sun, as observed by Gaia data release 3 (Gaia DR3). Meanwhile, the GALAH DR4 survey has spectroscopically characterised nearly one million stars, delivering detailed chemical abundances (up to 30 elements). We present a joint analysis of the $\sim$ 6 000 stars common to both catalogues, offering initial insights into the stellar and chemical properties of the solar neighborhood. Our preliminary results indicate that the majority of these stars are FGK main-sequence objects, with some A-type interlopers (with effective temperatures ranging between 3 000 and 8 000 K), with median ages of $\sim$ 1.6 Gyr (ranging from 0.10 to 14.79 Gyr), and metal-poorer when compared to the Sun: [Fe/H] $\approx$ -0.19 dex. Additionally, most of the stars are disc members, with some local halo (high-velocity) stars identified. Building on this foundation, future work will deeper exploit the full spectroscopic information and orbital parameters from value-added catalogues to refine Galactic component classifications (thin-thick disc versus halo membership), perform detailed chemical profiling, and deliver a comprehensive chemo-dynamical characterisation of the solar neighborhood. This will provide new insights into the formation and evolution of nearby stellar populations.

Figures (4)

• Figure 1: [Fe/H] (right) and [Mg/Fe] (left) distributions of our sample.
• Figure 2: Kiel diagram and age distribution of our sample. Left panel: Kiel diagram with PARSEC isochrones overlaid Bressan2012 centred at $\sim$ 1.6 Gyr and [Fe/H] $\approx -0.19$ dex (median values of our sample; green), and $\pm1 \sigma$ (cyan and blue) at fixed median [Fe/H]. For reference, the full GALAH DR4 is shown in yellow, while our targets are in red. Right panel: stellar age distribution of our sample.
• Figure 3: Toomre diagram, with concentric circles centred at 232.8 $\rm{km\,s^{-1}}$ marking velocity thresholds in 50 $\rm{km\,s^{-1}}$ steps. Velocities were corrected using the Solar motion $(U_\odot, V_\odot, W_\odot) = (8.6 \pm 0.9,\, 13.9 \pm 1.0,\, 7.1 \pm 1.0)$$\rm{km\,s^{-1}}$McMillan2017. Stars exceeding 100 $\rm{km\,s^{-1}}$ relative to the Sun are likely local halo members (228 stars), while the majority correspond to the Galactic disc (a total of 5970 stars). A small fraction (24 corresponding to 0.39% of the solar total sample) of high-velocity stars were omitted to enhance clarity.
• Figure 4: Tinsley--Wallerstein diagram, showing the separation between thin and thick disc populations following RecioBlanco2014, with the boundary smoothed using a quadratic spline as described in Dantas2025a. Grey points lie within 1$\sigma$ of the spline boundary. Stars most likely belonging to the thin disc are shown in shades of red and those more likely belonging to the thick disc are in yellow, with opacity reflecting classification confidence (1–2$\sigma$).