Detection of ${}^7$Be II in the Small Magellanic Cloud

Abstract

We analyse high resolution spectra of two classical novae that exploded in the Small Magellanic Cloud. ${}^7$Be 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 ${}^7$Be formation, are effective also in the low metallicity regime, characteristic of the SMC. Derived yields are of N(${}^7$Be=${}^7$Li)/N(H) = (5.3 $\pm$ 0.2) $\times$ 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 ${}^7$Be and similar yields. For an ejecta of $M_{H,ej}=$ 10${}^{-5}$ M${}_{\odot }$, the amount of ${}^7$Li produced is of $M_{{}^{7}Li}=(3.7\pm 0.6)\times 10^{-10}$ M${}_{\odot }$ 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) $\approx$ 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.

13 pages, 17 figures, 4 tables. Accepted for publication in MNRAS

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• 7Be detection in the 2021 outburst of RS Oph
• Lithium in coalesced non-compact stars
• Extragalactic 85Rb/87Rb and 6Li/7Li ratios in the Small Magellanic Cloud
• The cosmological lithium problem
• Galaxy Formation and Symbiotic Evolution with the Inter-Galactic Medium in the Age of ELT-ANDES
• Gaia-Sausage-Enceladus: Lithium evolution from early red-giant-branch and main-sequence stars
• Viability of novae as sources of Galactic lithium