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Abstract We present stellar parameters and chemical abundances of 47 elements detected in the bright (V= 11.63) very metal-poor ([Fe/H] = −2.20 ± 0.12) star 2MASS J22132050−5137385. We observed this star using the Magellan Inamori Kyocera Echelle spectrograph as part of ongoing work by theR-Process Alliance. The spectrum of 2MASS J22132050−5137385 exhibits unusually strong lines of elements heavier than the iron group, and our analysis reveals that these elements were produced by rapid neutron-capture (r-process) nucleosynthesis. We derive a europium enhancement, [Eu/Fe] = +2.45 ± 0.08, that is higher than any otherr-process-enhanced star known at present. This star is only the eighthr-process-enhanced star where both thorium and uranium are detected, and we calculate the age of ther-process material, 13.6 ± 2.6 Gyr, from the radioactive decay of these isotopes. This star contains relatively large enhancements of elements that may be produced as transuranic fission fragments, and we propose a new method using this characteristic to assess ther-process yields and gas dilution in samples ofr-process-enhanced stars. Assuming a canonical baryonic minihalo mass of 10⁶M_⊙and a 1% metal retention rate, this star formed in a cloud of only ∼600M_⊙. We conclude that 2MASS J22132050−5137385 exhibits a high level ofr-process enhancement because it formed in an environment where ther-process material was less diluted than average. 

Abstract We present the discovery of 2MASS J05241392−0336543 (hereafter J0524−0336), a very metal-poor ([Fe/H] = −2.43 ± 0.16), highlyr-process-enhanced ([Eu/Fe] = +1.34 ± 0.10) Milky Way halo field red giant star, with an ultrahigh Li abundance ofA(Li, 3D, NLTE) = 6.15 ± 0.25 and [Li/Fe] = +7.64 ± 0.25, respectively. This makes J0524−0336 the most lithium-enhanced giant star discovered to date. We present a detailed analysis of the star’s atmospheric stellar parameters and chemical abundance determinations. Additionally, we detect indications of infrared excess, as well as observe variable emission in the wings of the Hαabsorption line across multiple epochs, indicative of a potential enhanced mass-loss event with possible outflows. Our analysis reveals that J0524−0336 lies either between the bump and the tip of the red giant branch (RGB), or on the early asymptotic giant branch (e-AGB). We investigate the possible sources of lithium enrichment in J0524−0336, including both internal and external sources. Based on current models and on the observational evidence we have collected, our study shows that J0524−0336 may be undergoing the so-called lithium flash that is expected to occur in low-mass stars when they reach the RGB bump and/or the e-AGB. 

Abstract M15 is a globular cluster with a known spread in neutron-capture elements. This paper presents abundances of neutron-capture elements for 62 stars in M15. Spectra were obtained with the Michigan/Magellan Fiber System spectrograph, covering a wavelength range from ∼4430 to 4630 Å. Spectral lines from Fei, Feii, Sri, Zrii, Baii, Laii, Ceii, Ndii, Smii, Euii, and Dyii were measured, enabling classifications and neutron-capture abundance patterns for the stars. Of the 62 targets, 44 are found to be highly Eu-enhancedr-II stars, another 17 are moderately Eu-enhancedr-I stars, and one star is found to have ans-process signature. The neutron-capture patterns indicate that the majority of the stars are consistent with enrichment by ther-process. The 62 target stars are found to show significant star-to-star spreads in Sr, Zr, Ba, La, Ce, Nd, Sm, Eu, and Dy, but no significant spread in Fe. The neutron-capture abundances are further found to have slight correlations with sodium abundances from the literature, unlike what has been previously found; follow-up studies are needed to verify this result. The findings in this paper suggest that the Eu-enhanced stars in M15 were enhanced by the same process, that the nucleosynthetic source of this Eu pollution was ther-process, and that ther-process source occurred as the first generation of cluster stars was forming.