Detection of 7Be II in the Small Magellanic Cloud
Date Issued
2022
Author(s)
•
•
Gabriele Cescutti
•
Elias Aydi
•
•
Eamonn Harvey
•
Adriano Agnello
•
Piercarlo Bonifacio
•
•
Ernesto Guido
•
Margarita Hernanz
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.
Volume
510
Issue
4
Start page
5302
Issn Identifier
0035-8711
Rights
open.access
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