Heavy Elements in the Early Galaxy

TL;DR

This study investigates the chemical compositions of ancient metal-poor stars to understand early galactic nucleosynthesis, finding that certain element enhancements are not due to binary mass transfer but likely originate from supernova processes.

Contribution

It provides observational evidence that r-process and carbon enhancements in EMP stars are not caused by binary mass transfer, shedding light on early universe nucleosynthesis.

Findings

Most EMP stars follow a normal element ratio pattern.

10-15% of EMP stars are enriched in heavy neutron-capture elements.

Radial velocity data suggests enhancements are not from binary companions.

Abstract

The oldest stars in the universe retain to a great extent detailed information on the chemical composition of the interstellar medium at the time of their birth. Hence the earliest phases of Galactic chemical evolution and nucleosynthesis in the early universe can be investigated by means of the old metal-poor stars. For the majority of extremely metal-poor (EMP) stars the element ratios follow a normal pattern, but 10-15% of the stars are enhanced in heavy neutron-capture (r- or s-processes) elements by large factors, and about 20% are strongly enriched in carbon. The enhancement of some elements could be the result of highly non-spherical supernova and inefficient mixing in the early interstellar medium. Alternative, they could be due to mass transfer from a former AGB or supernova binary companion that has now evolved to a white dwarf or neutron star. If the latter explanation is true we can detect these stars as long-period binaries. Radial velocity monitoring over a period of ~5 years of a sample of EMP stars with either r-process element and/or carbon enhancement is presented. The results indicate that pure r-process and carbon enhancements are not results of mass transfer from a binary companion.