The hydrogen-deficient [ WCL ] type central star HD167362 and its planetary nebula ( PN ) SwSt 1 are investigated .
The central star has a carbon-rich emission line spectrum and yet the nebula exhibits a 10- \mu m emission feature from warm silicate dust , perhaps indicating a recent origin for the carbon-rich stellar spectrum .
Its stellar and nebular properties might therefore provide further understanding as to the origin of the [ WCL ] central star class .

The central star optical and UV spectra are modelled with state of the art non-LTE codes for expanding atmospheres , from which the stellar parameters are determined .
Using the Sobolev approximation code isa -Wind , we find T _ { eff } =40 000 K , log ( { \dot { M } } /M _ { \odot } yr ^ { -1 } ) =–6.72 , L=8900 L _ { \odot } ( for a distance of 2.0 kpc ) , and v _ { \infty } \simeq 900 km s ^ { -1 } .
The abundance mass fractions for helium , carbon and oxygen is determined to be 37 % , 51 % and 12 % , respectively .
From this we derive C/O=4.3 ( by mass ) , confirming that the star suffered efficient third dredge-up .
The nitrogen abundance is close to zero , while an upper limit of < 10 % by mass is established for H. The model uses a composite beta velocity law which allows us to reproduce the optical line profiles .
The overall shape of the de-reddened spectrum agrees with the V-scaled ( m _ { V } =11.48 mag , E ( B–V ) =0.46 mag ) model atmosphere , showing the nebular-derived reddening to be consistent with the reddening indicated by the stellar analysis .
We confirm our model results by using the co-moving frame code cmfgen , although a few differences remain .

The PN has a high electron density ( log ( N _ { e } /cm ^ { -3 } ) =4.5 ) and a small ionized radius ( 0.65 arcsec - measured from the HST-WF/PC H \beta images ) , indicating a young object .
Its nebular abundances are not peculiar .
The nebular C/O ratio is close to solar , confirming the PN as an O-rich nebula .
The nebular N/O ratio of 0.08 is not indicative of a Type-I PN although the high stellar luminosity points to a relatively stellar mass .
Near-IR spectroscopy is presented and fitted together with IRAS fluxes by using two blackbody curves with temperatures 1200 K and 230 K , indicating the presence of hot dust .
We also report the first detection of H _ { 2 } in this young and compact PN .

All of the published spectroscopy since the discovery of SwSt 1 in 1895 has been re-examined and it is concluded that no clear spectral variability is seen , in contrast to claims in some previously-published studies .
If an event occurred that has turned it into a hydrogen-deficient central star , it did not happen in the last 100 years .