  Hot subdwarfs represent a group of low-mass helium-burning stars formed
through binary-star interactions and include some of the most
chemically-peculiar stars in the Galaxy. Stellar evolution theory suggests that
they should have helium-rich atmospheres but, because radiation causes hydrogen
to diffuse upwards, a majority are extremely helium poor. Questions posed
include: when does the atmosphere become chemically stratified and at what
rate?
  The existence of several helium-rich subdwarfs suggests further questions;
are there distinct subgroups of hot subdwarf, or do hot subdwarfs change their
surface composition in the course of evolution? Recent analyses have revealed
remarkable surface chemistries amongst the helium-rich subgroup. In this paper,
we analyse high-resolution spectra of nine intermediate helium-rich hot
subdwarfs. We report the discovery that two stars, HE 2359-2844 and HE
1256-2738, show an atmospheric abundance of lead which is nearly ten thousand
times that seen in the Sun. This is measured from optical Pb IV absorption
lines never previously seen in any star. The lead abundance is ten to 100 times
that measured in normal hot subdwarf atmospheres from ultraviolet spectroscopy.
HE 2359-2844 also shows zirconium and yttrium abundances similar to those in
the zirconium star LS IV-14 116. The new discoveries are interpreted in terms
of heavily stratified atmospheres and the general picture of a surface
chemistry in transition from a new-born helium-rich subdwarf to a normal
helium-poor subdwarf.
