Search for 7Be in the outburst of four recent novae

Following the recent detection of 7Be in the outburst spectra of Classical Novae we report the search for this isotope in the outbursts of four recent bright novae by means of high resolution UVES observations. The 7BeII 313.0583, 313.1228 nm doublet resonance lines are detected in the high velocity components of Nova Mus 2018 and ASASSN-18fv during outburst. On the other hand 7BeII is neither detected in ASASSN-17hx and possibly nor in Nova Cir 2018, therefore showing that the 7BeII is not always ejected in the thermonuclear runaway. Taking into account the 7Be decay we find X(7Be)/X(H) approx 1.5 x10 ^{-5} and 2.2 x 10 ^{-5} in Nova Mus 2018 and ASASSN-18fv, respectively. A value of 7Be/H about 2 x10 ^{-5} is found in 5 out of the 7 extant measurements and it might be considered as a typical 7Be yield for novae. However, this value is almost one order of magnitude larger than predicted by current theoretical models. We argue that the variety of high 7Be/H abundances could be originated in a higher than solar content of 3He in the donor star. The cases with 7Be not detected might be related to a small mass of the WD or to relatively little mixing with the core material of the WD. The 7Be /H, or 7Li/H, abundance is about 4 dex above meteoritic thus confirming the novae as the main sources of 7Li in the Milky Way.