# The lowest detected stellar Fe abundance: The halo star SMSS J160540.18-144323.1

## TL;DR

This paper reports the discovery of the most iron-deficient star known, SMSS J160540.18-144323.1, which provides insights into the early universe and Population III supernovae through its unique chemical composition.

## Contribution

The paper presents the discovery and detailed chemical analysis of the lowest iron abundance star, offering new constraints on early stellar evolution and supernova models.

## Key findings

- Star has [Fe/H] = -6.2, the lowest detected iron abundance.
- Star is strongly carbon-enhanced with [C/Fe] = 3.9.
- Abundance pattern suggests origin from low-energy Population III supernovae.

## Abstract

We report the discovery of SMSS J160540.18-144323.1, a new ultra-metal poor halo star discovered with the SkyMapper telescope. We measure [Fe/H] = -6.2 +- 0.2 (1D LTE), the lowest ever detected abundance of iron in a star. The star is strongly carbon-enhanced, [C/Fe] = 3.9 +- 0.2, while other abundances are compatible with an alpha-enhanced solar-like pattern with [Ca/Fe] = 0.4 +- 0.2, [Mg/Fe] = 0.6 +- 0.2, [Ti/Fe] = 0.8 +- 0.2, and no significant s- or r-process enrichment, [Sr/Fe] < 0.2 and [Ba/Fe] < 1.0 (3{\sigma} limits). Population III stars exploding as fallback supernovae may explain both the strong carbon enhancement and the apparent lack of enhancement of odd-Z and neutron-capture element abundances. Grids of supernova models computed for metal-free progenitor stars yield good matches for stars of about 10 solar mass imparting a low kinetic energy on the supernova ejecta, while models for stars more massive than roughly 20 solar mass are incompatible with the observed abundance pattern.