SD 1313-0019 -- Another second-generation star with [Fe/H] = -5.0, observed with the Magellan Telescope

TL;DR

This paper reports the detailed chemical analysis of a second-generation star with extremely low iron content ([Fe/H] = -5.0), revealing insights into early stellar populations and supernova yields.

Contribution

It provides high-resolution spectroscopic data of a star with [Fe/H] = -5.0 and models its progenitor as a 20-30 solar mass Population III supernova, expanding knowledge of early star formation.

Findings

Star has [Fe/H] = -5.0 and high carbon enhancement.

Elemental abundances align with yields from a 20-30 M_sun Population III supernova.

Supports the idea that early massive stars enriched the universe with carbon.

Abstract

We present a Magellan/MIKE high-resolution (R ~ 35,000) spectrum of the ancient star SD 1313-0019 which has an iron abundance of [Fe/H] = -5.0, paired with a carbon enhancement of [C/Fe] ~ 3.0. The star was initially identified by Allende Prieto et al. in the BOSS survey. Its medium-resolution spectrum suggested a higher metallicity of [Fe/H] = -4.3 due to the CaII K line blending with a CH feature which is a common issue related to the search for the most iron-poor stars. This star joins several other, similar stars with [Fe/H] < -5.0 that all display a combination of low iron and high carbon abundances. Other elemental abundances of SD 1313-0019 follow that of more metal-rich halo stars. From fitting the abundance pattern with yields of Population III supernova, we conclude that SD 1313-0019 had only one massive progenitor star with 20 - 30 M_sun that must have undergone a mixing and fallback episode. Overall, there are now five stars known with [Fe/H] < -5.0 (1D LTE abundances). This population of second-generation stars strongly suggests massive first stars that almost exclusively produced large amounts of carbon through stellar winds and/or their mixing and fallback supernova explosions. As a consequence, their natal clouds -- presumably some early minihalo structures -- contained ample amounts of carbon and oxygen that likely facilitated the formation of these first low-mass stars.