  The sharp-line spectrum of the Bp star HR 6000 has peculiarities that
distinguish it from those of the HgMn stars with which it is sometimes
associated. The position of the star close to the center of the Lupus 3
molecular cloud, whose estimated age is on the order of 9.1 +/- 2.1 Myr, has
lead to the hypothesis that the anomalous peculiarities of HR 6000 can be
explained by the young age of the star. Observational material from HST
provides the opportunity to extend the abundance analysis previously performed
for the optical region and clarify the properties of this remarkable peculiar
star. Our aim was to obtain the atmospheric abundances for all the elements
observed in a broad region from 1250 to 10000 A. An LTE synthetic spectrum was
compared with a high-resolution spectrum observed with STIS equipment in the
1250-3040 A interval. The adopted model is an ATLAS12 model already used for
the abundance analysis of a high-resolution optical spectrum observed at ESO
with UVES. The stellar parameters are Teff=13450K, logg=4.3, and zero
microturbulent velocity. Abundances for 28 elements and 7 upper limits were
derived from the ultraviolet spectrum. Adding results from previous work, we
have now quantitative results for 37 elements, some of which show striking
contrasts with those of a broad sample of HgMn stars. The analysis has pointed
out ionization anomalies and line-to-line variation in the derived abundances,
in particular for silicon. The inferred discrepancies could be explained by
non-LTE effects and with the occurrence of diffusion and vertical abundance
stratification. In the framework of the last hypothesis, we obtained, by means
of trial and error, empirical step functions of abundance versus optical depth
log(tau_5000) for carbon, silicon, manganese, and gold, while we failed to find
such a function for phosphorous.
