uvby(-$\beta$) photometry of high-velocity and metal-poor stars X. Stars of very low metal abundance: observations, reddenings, metallicities, classifications, distances, and relative ages

TL;DR

This study presents uvby(-β) photometry for 411 very metal-poor stars, deriving their fundamental parameters and discussing their implications for Galactic evolution, including evidence for younger metal-poor stars and possible accretion events.

Contribution

It provides new photometric data and analysis for a large sample of very metal-poor stars, highlighting their ages and potential origins in Galactic formation processes.

Findings

Identification of field stars 1-3 Gyrs younger than M92

Evidence for hierarchical star formation and accretion events

Comparison of stars with globular cluster M92

Abstract

uvby(--$\beta$) photometry has been obtained for an additional 411 very metal-poor stars selected from the HK survey, and used to derive basic parameters such as interstellar reddenings, metallicities, photometric classifications, distances, and relative ages... These very metal-poor stars are compared to M92 in the c_0,(b-y)_0 diagram, and evidence is seen for field stars 1-3 Gyrs younger than this globular cluster. The significance of these younger very metal-poor stars is discussed in the context of Galactic evolution, mentioning such possibilities as hierarchical star-formation/mass-infall of very metal-poor material and/or accretion events whereby this material has been acquired from other (dwarf) galaxies with different formation and chemical-enrichment histories