HE0144-4657: A Carbon-Enhanced Ultra Metal-Poor Star ([Fe/H] ~ -4.1) from the Helmi Stream Disrupted Dwarf Galaxy

TL;DR

We discovered HE0144-4657, an ultra metal-poor, carbon-enhanced star linked to a disrupted dwarf galaxy, providing insights into early star formation and galaxy assembly.

Contribution

This is the first ultra metal-poor star found in a stellar stream, suggesting extragalactic origins of such stars and their formation in dwarf galaxy environments.

Findings

HE0144-4657 has [Fe/H] = -4.11, the lowest in a stellar stream.

Its chemical pattern indicates a second-generation star with a Population III progenitor.

The star likely formed in an accreted ultra-faint dwarf galaxy.

Abstract

We present the discovery of HE0144-4657, an ultra metal-poor, CNO-enhanced star dynamically associated with the Helmi Stream disrupted dwarf-galaxy remnant. This star was first identified as a carbon-enhanced, metal-poor star candidate from the Hamburg/ESO objective-prism survey, then followed up with medium- and high-resolution spectroscopy. At [Fe/H]=-4.11, HE0144-4657 is the lowest metallicity star found in a stellar stream to date. Its chemistry is consistent with field halo stars in the same metallicity regime, and the light-element (atomic number Z<=30) chemical abundance pattern suggests that HE0144-4657 is a bona-fide second-generation star with a possible Population III progenitor in the 50Msun mass range with low explosion energy. One possible scenario for the origin of HE0144-4657 is that it was formed in an ultra-faint dwarf galaxy accreted by the Helmi Stream progenitor system before merging with the Milky Way. This discovery provides further evidence for the extragalactic origin of carbon-enhanced ultra metal-poor stars in the Milky Way and for the specific environments conducive to their formation.