Be-7 detection in the 2021 outburst of RS Oph

The recurrent nova RS Oph underwent a new outburst on 2021 August 8, reaching a visible brightness of V = 4.8 mag. Observations of the 2021 outburst made with the high-resolution UVES spectrograph at the Kueyen-UT2 telescope at ESO-VLT in Parana) enabled detection of the possible presence of Be-7 newly made in the thermonuclear runaway reactions. The Be-7 yields can be estimated at N(Be-7)/N(H) = 5.7 x 10(-6), which are close to the lowest yields measured in classical novae so far. Be-7 is short-lived and decays only into Li-7. By means of a spectrum taken during the nebular phase we estimated an ejected mass of approximate to 1.1 x 10(-5) M-circle dot, providing an amount of approximate to 4.4 x 10(-10) M-circle dot of Li-7 created in the 2021 event. Recurrent novae of the RS Oph type may synthesize slightly lower amounts of Li-7 per event than classical novae, but occur 10(3) times more frequently. The recurrent novae fraction is in the range of 10-30 per cent and they could have contributed to the making of the Li-7 that we observe today. The detection of Be-7 in RS Oph provides further support to the recent suggestion that novae are the most effective source of Li-7 in the Galaxy.