Chemical compositions and kinematics of the Hercules stream

TL;DR

This study analyzes the chemical compositions and kinematics of 58 K giants in the Hercules stream, revealing it is predominantly composed of metal-rich thin disc stars with compositions similar to the Galactic thin disc.

Contribution

It provides detailed abundance analysis of Hercules stream giants and compares their metallicity distribution with FG dwarf surveys, clarifying the stream's stellar population.

Findings

The giants have [Fe/H] from -0.17 to +0.42, averaging +0.15.

The stream's composition resembles the Galactic thin disc.

The stream is mainly composed of metal-rich thin disc stars.

Abstract

An abundance analysis is reported of 58 K giants identified by Famaey et al. (2005) as highly probable members of the Hercules stream selected from stars north of the celestial equator in the Hipparcos catalogue. The giants have compositions spanning the interval [Fe/H] from $-$0.17 to $+$0.42 with a mean value of $+$0.15 and relative elemental abundances [El/Fe] representative of the Galactic thin disc. Selection effects may have biassed the selection from the Hipparcos catalogue against the selection of metal-poor stars. Our reconsideration of the recent extensive survey of FG dwarfs which included metal-poor stars (Bensby et al. 2014) provides a [Fe/H] distribution for the Hercules stream which is similar to that from the 58 giants. It appears that the stream is dominated by metal-rich stars from the thin disc. Suggestions in the literature that the stream includes metal-poor stars from the thick disc are discussed.