2023MNRAS.518.2614M

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 Paranal enabled detection of the possible presence of ⁷Be newly made in the thermonuclear runaway reactions. The ⁷Be yields can be estimated at N(⁷Be)/N(H) = 5.7 × 10^–6, which are close to the lowest yields measured in classical novae so far. ⁷Be is short-lived and decays only into ⁷Li. By means of a spectrum taken during the nebular phase we estimated an ejected mass of ≈ 1.1 × 10^–5 M_⊙, providing an amount of ≈ 4.4 × 10^–10 M_⊙ of ⁷Li created in the 2021 event. Recurrent novae of the RS Oph type may synthesize slightly lower amounts of ⁷Li per event than classical novae, but occur 10³ 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 ⁷Li that we observe today. The detection of ⁷Be in RS Oph provides further support to the recent suggestion that novae are the most effective source of ⁷Li in the Galaxy.