Abstract
Context. Measurable amounts of Be could have been synthesised primordially if the Universe were non-homogeneous or in the presence of late decaying relic particles. Aims. 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. Methods. High resolution, high signal-to-noise ratio (S/N) 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. Results. 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. Conclusions. Our observation reinforces the existing upper limit on primordial Be. There is no observational indication for a primordial production of 9Be. 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.
Highlights
Beryllium has only one stable isotope, 9Be
In this paper we present the analysis of high signal-to-noise ratio (S/N) UV spectra of the star 2MASS J1808-5104 acquired with the specific aim of investigating its Be abundance
In order to observe the Be line at 313 nm, new spectra of the ultra metal-poor (UMP) dwarf 2MASS J1808-5104 were obtained in June 2018 with the Very Large Telescope (VLT) and the spectrograph UVES (Dekker et al 2000)
Summary
Beryllium has only one stable isotope, 9Be. The lack of stable nuclei with A = 5 implies that it cannot be synthesised by capture of α particles and the lack of stable nuclei with A = 8 implies that it cannot be synthesised by proton nor neutron captures either. If the primordial plasma was inhomogeneous and in particular included lower density n-rich regions, Boyd & Kajino (1989) showed that 3H and 7Li could be abundant enough to make the 7Li(3H, n)9Be reaction, which is an efficient channel to produce sizeable amounts of 9Be. A way to introduce new physics is to postulate the existence of relic particles, interacting either electromagnetically or strongly, which decay at late times Pospelov & Pradler (2011) showed that the energy injected by decaying hadrons can lead to an efficient 9Be production via the 6He(4He, n)9Be reaction They advocate the use of an upper limit on the primordial 9Be abundance as a powerful test to put limits on the energy and decay half-life of such putative relic hadrons. In this paper we present the analysis of high signal-to-noise ratio (S/N) UV spectra of the star 2MASS J1808-5104 acquired with the specific aim of investigating its Be abundance
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