# Be and O in the ultra metal-poor dwarf 2MASS J18082002-5104378: The Be-O correlation

## TL;DR

This study measures beryllium and oxygen abundances in an extremely metal-poor star to constrain primordial nucleosynthesis and the early Galaxy's chemical evolution, finding no evidence for primordial Be and suggesting a breakdown of the Be-O relation.

## Contribution

First measurement of Be in an ultra metal-poor star, providing constraints on primordial nucleosynthesis and early Galactic chemical processes.

## Key findings

- No observational evidence for primordial Be production.
- Upper limit on Be abundance supports a homogeneous early Universe.
- Be-O relation may break down in the early Galaxy.

## Abstract

Measurable amounts of Be could have been synthesised primordially if the Universe were non-homogeneous or in the presence of late decaying relic particles. We investigate the Be abundance in the extremely metal-poor star 2MASS J1808-5104 ([Fe/H]=--3.84) with the aim of constraining inhomogeneities or the presence of late decaying particles. High resolution, high signal-to-noise ratio UV spectra were acquired at ESO with the Kueyen 8.2 m telescope and the UVES spectrograph. Abundances were derived using several model atmospheres and spectral synthesis code. We measured log(Be/H) = -14.3 from a spectrum synthesis of the region of the Be line. Using a conservative approach, however we adopted an upper limit two times higher, i.e. log(Be/H) < -14.0. We measured the O abundance from UV OH lines and find [O/H]=--3.46 after a 3D correction. Our observation reinforces the existing upper limit on primordial Be. There is no observational indication for a primordial production of Be. This places strong constraints on the properties of putative relic particles. This result also supports the hypothesis of a homogeneous Universe, at the time of nucleosynthesis. Surprisingly, our upper limit of the Be abundance is well below the Be measurements in stars of similar [O/H]. This may be evidence that the Be-O relation breaks down in the early Galaxy, perhaps due to the escape of spallation products from the gas clouds in which stars such as 2MASS J1808-5104 have formed.