Barium - rich G stars in the nuclei of the planetary nebulae Abell 35 and LoTr 5 ?

A spectroscopic analysis of the G-star located at the centre of Abell 35 leads to a surface gravity log g= 3.7±0.5 and an effective temperature T eff = 5300 ± 200 K, which are typical of a G8IV spectral type. We estimate a projected rota-tional velocity of 55 ± 10 km s −1 and deduce a radius 1.5 ≤ R G ≤ 3.5R in agreement with the subgiant luminosity class: the star is rapidly rotating, near the break-up as for LoTr5 (Jas-niewicz et al. 1996a). For both late-type central stars of Abell 35 and LoTr5, we show a photospheric enhancement of the barium element which can be understood as caused by the transfer of s-process-overabundant material from the former AGB star which is now the hot star of the binary. These G-stars could be pre-barium stars in detached binary systems.