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Abstract The ultrafaint dwarf galaxy Reticulum II was enriched by a single rare and prolific r -process event. The r -process content of Reticulum II thus provides a unique opportunity to study metal mixing in a relic first galaxy. Using multi-object high-resolution spectroscopy with VLT/GIRAFFE and Magellan/M2FS, we identify 32 clear spectroscopic member stars and measure abundances of Mg, Ca, Fe, and Ba where possible. We find 72 − 12 + 10 % of the stars are r -process-enhanced, with a mean [ Ba / H ] = − 1.68 ± 0.07 and unresolved intrinsic dispersion σ [Ba/H] <0.20. The homogeneous r -process abundances imply that Ret II’s metals are well mixed by the time the r -enhanced stars form, which simulations have shown requires at least 100 Myr of metal mixing in between bursts of star formation to homogenize. This is the first direct evidence of bursty star formation in an ultrafaint dwarf galaxy. The homogeneous dilution prefers a prompt and high-yield r -process site, such as collapsar disk winds or prompt neutron star mergers. We also find evidence from [Ba/H] and [Mg/Ca] that the r -enhanced stars in Ret II formed in the absence of substantial pristine gas accretion, perhaps indicating that ≈70% of Ret II stars formed after reionization. 

We analyse high-resolution spectra of two classical novae that exploded in the Small Magellanic Cloud (SMC). 7Be ii resonance transitions are detected in both ASASSN-19qv and ASASSN-20ni novae. This is the first detection outside the Galaxy and confirms that thermo-nuclear runaway reactions, leading to the 7Be formation, are effective also in the low-metallicity regime, characteristic of the SMC. Derived yields are of N(7Be = 7Li)/N(H)  = (5.3 ± 0.2) × 10−6 which are a factor 4 lower than the typical values of the Galaxy. Inspection of two historical novae in the Large Magellanic Cloud observed with IUE in 1991 and 1992 showed also the possible presence of 7Be and similar yields. For an ejecta of MH, ej = 10−5 M⊙, the amount of 7Li produced is of $M_{^7 Li} = (3.7 \pm 0.6) \times 10^{-10}$ M⊙ per nova event. Detailed chemical evolutionary model for the SMC shows that novae could have made an amount of lithium in the SMC corresponding to a fractional abundance of A(Li) ≈ 2.6. Therefore, it is argued that a comparison with the abundance of Li in the SMC, as measured by its interstellar medium, could effectively constrain the amount of the initial abundance of primordial Li, which is currently controversial.