Aconsiderablefractionofthecentralstarsofplanetarynebulæ ( CSPNe ) arehydrogen-deficient.Asarule , theseCSPNeexhibitachemicalcompositionofhelium , carbon , andoxygenwiththemajorityshowingWolf-Rayet-likeemissionlinespectra.ThesestarsareclassifiedasCSPNeofaspectraltype [ WC ] .WeperformaspectralanalysisofCSPNPB 8withthePotsdamWolf-Rayet ( PoWR ) modelsforexpandingatmospheres.ThesourcePB 8displayswind-broadenedemissionlinesfromstrongmassloss.Moststrikingly , wefindthatitssurfacecompositionishydrogen-deficient , butnotcarbon-rich.Withmassfractionsof55 % helium,40 % hydrogen,1.3 % carbon,2 % nitrogen , and1.3 % oxygen , itdiffersgreatlyfromthe30–50 % ofcarbonwhicharetypicallyseenin [ WC ] -typecentralstars.TheatmosphericmixtureinPB 8hasananalogyintheWN/WCtransitiontypeamongthemassiveWolf-Rayetstars.Thereforewesuggesttointroduceanewspectraltype [ WN/WC ] forCSPNe , withPB 8asitsfirstmember.ThecentralstarofPB 8hasarelativelylowtemperatureof T _ { * } = 52 \text { kK } , asexpectedforcentralstarsintheirearlyevolutionarystages.Itssurroundingnebulaislessthan3000yearsold , i.e .
relativelyyoung.Existingcalculationsforthepost-AGBevolutioncanproducehydrogen-deficientstarsofthe [ WC ] type , butdonotpredictthecompositionfoundinPB 8.Wediscussvariousscenariosthatmightexplaintheoriginofthisuniqueobject .