Local stars formed at z>10: a sample extracted from the SDSS

TL;DR

This paper reports the discovery and detailed chemical analysis of extremely metal-poor stars formed at redshift greater than 10, using SDSS data and high-resolution follow-up, providing insights into the early universe's star formation.

Contribution

It introduces a new automated analysis tool, MyGIsFOS, and presents the first detailed chemical abundances of stars formed at z>10 from SDSS data.

Findings

Identification of EMP star candidates from SDSS spectra.

High-resolution follow-up confirms extremely low metallicity.

Chemical abundance patterns provide constraints on first star properties.

Abstract

As the Universe emerged from its initial hot and dense phase, its chemical composition was extremely simple, being limited to stable H and He isotopes, and traces of Li. The first stars that formed had such initial composition. However, they quickly began to produce a whole array of heavier nuclei, polluting the interstellar medium. While none among these first stars has been detected to date, an increasing sample exists of their direct descendant, stars with heavy elements content of the order of 1/1000 of the solar value, or less. In most cases, such stars should have formed at redshift of about 10 or beyond, and their chemical composition can provide crucial constraints to the nature of the very first stars. Extremely metal poor (EMP) stars are exceedingly rare. We used the low resolution spectra obtained by the Sloan Digital Sky Survey (SDSS) to search for EMP candidates: results of VLT-UVES high resolution follow-up for 16 of them is presented here. A newly developed automatic abundance analysis and parameter determination code, MyGIsFOS, has been employed to analyze the detailed chemical abundances of such stars.