  The ultraviolet spectra of all ``weak emission line central stars of
planetary nebulae'' (WELS) with available IUE data are presented and discussed.
We performed line identifications, equivalent width and flux measurements for
several features in their spectra. We found that the WELS can be divided in
three different groups regarding their UV: i) Strong P-Cygni profiles (mainly
in CIV 1549); ii) Weak P-Cygni features and iii) Absence of P-Cygni profiles.
The last group encompasses stars with a featureless UV spectrum or with intense
emission lines and a weak continuum, which are most likely of nebular origin.
We have measured wind terminal velocities for all objects presenting P-Cygni
profiles in N V 1238 and/or C IV 1549. The results obtained were compared to
the UV data of the two prototype stars of the [WC]-PG 1159 class, namely, A30
and A78. For WELS presenting P-Cygnis, most of the terminal velocities fall in
the range ~1000-1500 km/s, while [WC]-PG 1159 stars possess much higher values,
of about 3000 km/s. The [WC]-PG1159 stars are characterized by intense,
simultaneous P-Cygni emissions in the 1150-2000A interval of N V 1238, O V 1371
and C IV 1549. In contrast, we found that O V 1371 is very weak or absent in
the WELS spectra. On the basis of the ultraviolet spectra alone, our findings
indicate that [WC]-PG 1159 stars are distinct from the WELS, contrary to
previous claims in the literature.
