Bright Metal-Poor Stars from the Hamburg/ESO Survey. II. A Chemodynamical Analysis

TL;DR

This study provides a comprehensive chemodynamical analysis of 1777 bright metal-poor stars from the Hamburg/ESO Survey, revealing insights into their distribution, origins, and the prevalence of carbon-enhanced stars.

Contribution

It introduces a new spectroscopic pipeline to estimate stellar parameters for a large local sample, enabling detailed chemodynamical analysis and identification of stellar populations and streams.

Findings

Increase in CEMP stars with decreasing metallicity

Higher fraction of CEMP stars with distance from Galactic plane

Identification of CEMP stars with thick-disk kinematics

Abstract

We obtain estimates of stellar atmospheric parameters for a previously published sample of 1777 relatively bright (9 < B < 14) metal-poor candidates from the Hamburg/ESO Survey. The original Frebel et al. analysis of these stars was only able to derive estimates of [Fe/H] and [C/Fe] for a subset of the sample, due to limitations in the methodology then available. A new spectroscopic analysis pipeline has been used to obtain estimates of Teff, log g, [Fe/H], and [C/Fe] for almost the entire dataset. This sample is very local - about 90% of the stars are located within 0.5 kpc of the Sun. We consider the chemodynamical properties of these stars in concert with a similarly local sample of stars from a recent analysis of the Bidelman & MacConnell 'weak-metal' candidates by Beers et al. We use this combined sample to identify possible members of the suggested halo stream of stars by Helmi et al. and Chiba & Beers, as well as stars that may be associated with stripped debris from the putative parent dwarf of the globular cluster Omega Centauri, suggested to exist by previous authors. We identify a clear increase in the cumulative frequency of carbon-enhanced metal-poor (CEMP) stars with declining metallicity, as well as an increase in the fraction of CEMP stars with distance from the Galactic plane, consistent with previous results. We also identify a relatively large number of CEMP stars with kinematics consistent with the metal-weak thick-disk population, with possible implications for its origin.