1995A&A...297..779J

The highly variable star V 348Sgr has been variously described as a hot RCrB star, an extreme helium star and a cool Wolf-Rayet ([WC11]) central star of a planetary nebula. Despite the Wolf-Rayet nature of its spectrum, sufficient pure absorption lines are visible to allow the LTE analysis of its photosphere presented in this paper. The weak #1IVλ5801,12A doublet and the strong #1IIIλ4647,50,51A blend provide a sensitive measure of the carbon abundance. This analysis finds the surface parameters of V 348Sgr to be T_eff=22000K, logg≤2.7, n_C=0.10, logn_N=-3.7, logn_O=-3.5 and logn_Si=-5.1, where n are abundances by number fraction. These results are in reasonable agreement with a recent non-LTE analysis of the Wolf-Rayet spectrum (Leuenhagen & Hamann 1994A&A...283..567 [LH94]). The hydrogen abundance could not be determined from the present analysis; adopting n_H=0.20 after LH94, the helium abundance becomes n_He=0.70. The model flux distribution can be used to estimate the separate contributions of the interstellar and non-variable circumstellar extinction towards V 348Sgr; the former corresponds to a reddening E_B–V=0.63. Previous high carbon abundance models had predicted a strong CII opacity edge in the UV; the edge is sufficiently diluted by line-blanketing that the models now give a good fit to the observed flux distribution.

V348Sgr is confirmed to have a surface carbon abundance much higher than that encountered in extreme helium stars (typically n_C=0.01), but typical of other cool Wolf-Rayet central stars. However, the N/O and O/Si ratios are within the ranges observed in EHe and hot RCrB stars, implying that V 348Sgr and other [WC-L] stars may represent the C-rich extremity of an ubiquitous helium-star production mechanism. The analysis demonstrates the presence of CNO, 3α and ¹²C(α,γ)¹⁶O products, as well as a substantial hydrogen remnant, which imply that considerable disruption of the stellar surface layers must have occurred. Consequences for evolutionary models are considered.