Searching for the metal-weak thick disc in the solar neighbourhood

TL;DR

This study analyzes 60 nearby metal-poor stars to identify potential metal-weak thick disc stars using kinematic criteria, revealing a subset with very low metallicity that may belong to this elusive population.

Contribution

It provides the first detailed abundance analysis of a sample selected specifically to find metal-weak thick disc stars based on kinematic criteria.

Findings

14 stars meet the kinematic and metallicity criteria for metal-weak thick disc candidates.

6 stars have very low metallicity and may be metal-weak thick disc or halo stars.

The sample includes a mix of thick disc, halo, and hybrid stars, highlighting the complexity of stellar populations.

Abstract

An abundance analysis is presented of 60 metal-poor stars drawn from catalogues of nearby stars provided by Ariyanto et al. (2005) and Schuster et al. (2006). In an attempt to isolate a sample of metal-weak thick disc stars, we applied the kinematic criteria $V_{\rm rot} \geq 100$ km s$^{-1}$, $|U_{LSR}| \leq 140$ km s$^{-1}$, and $|W_{LSR}| \leq 100$ km s$^{-1}$. Fourteen stars satisfying these criteria and having [Fe/H] $\leq -1.0$ are included in the sample of 60 stars. Eight of the 14 have [Fe/H] $\geq -1.3$ and may be simply thick disc stars of slightly lower than average [Fe/H]. The other six have [Fe/H] from -1.3 to -2.3 and are either metal-weak thick disc stars or halo stars with kinematics mimicking those of the thick disc. The sample of 60 stars is completed by eight thick disc stars, 20 stars of a hybrid nature (halo or thick disc stars), and 18 stars with kinematics distinctive of the halo.