ИСТИНА

Only three symbiotic stars have ever demonstrated the resonance lithium line LiI 6707.8 Å. Two of them are well-known recurrent symbiotic novae (RSN) RS Oph and T CrB. The last one is a symbiotic Mira V407 Cyg. Wallerstein et al. (2008) reported that another 36 symbiotic stars (SS) undoubtedly do not show lithium lines. Mechanisms which can produce a sufficient amount of lithium in cool components’ atmospheres of these three SS are under discussion. Earlier we (2003) supposed that lithium enrichment in the symbiotic Mira V407 Cyg is due to Cameron-Fowler mechanism. Therefore a cool component of V407 Cyg must be an intermediate-mass asymptotic giant branch star on the hot bottom burning stage. Later Wallerstein et al. (2008) suggested the this mechanism for T CrB and RS Oph. But cool components of these RSN are RGB stars (not AGB stars)! In 2010 V407 Cyg underwent a very bright outburst RSN-type. Although another outburst of such type have not been detected during all observational history of V407 Cyg, it’s clear that these three systems have got once more common feature – the same type of activity. Now we suggest that the lithium enrichment in the cool components’ atmospheres of these SS may be due to RSN-type explosions on their hot components’ surfaces. Therefore LiI 6707.8 Å line may be variable on the orbital period timescale (because different sides of a cool component can obtained different amount of lithium from a hot component) as well as on the recurrence timescale (characteristic time between outbursts in RSN systems). This assumption requires high-resolution spectral observations of these three SS and two another RSN: V745 Sco and V3890 Sgr.