The infrared [WC] stars

A number of late [WC] stars have unique infrared properties, not found amon g the non-[WC] planetary nebulae, and together define a class of IR-[WC] st ars. They have unusual IRAS colours, resembling stars in the earliest post- AGB evolution and possibly related to PAH formation. Most or all show a dou ble chemistry, with both a neutral (molecular) oxygen-rich and an inner car bon-rich region. Their dense nebulae indicate recent evolution from the AGB , suggesting a fatal-thermal-pulse (FTP) scenario. Although both the colour s and the stellar characteristics predict fast evolution, it is shown that this phase must last for 10(4) yr. The morphologies of the nebulae are disc ussed. For one object in Sgr, the progenitor mass (1.3 M-.) is known. The s tellar temperatures of the IR-[WC] stars appear much higher in low metallic ity systems (LMC, Sgr). This may be indicative of an extended 'pseudo' phot osphere. It is proposed that re-accretion of ejected gas may slow down the post-AGB evolution and so extend the life time of the IR-[WC] stars.