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Hot subdwarfs represent a group of low-mass helium-burning stars formedthrough binary-star interactions and include some of the mostchemically-peculiar stars in the Galaxy. Stellar evolution theory suggests thatthey should have helium-rich atmospheres but, because radiation causes hydrogento diffuse upwards, a majority are extremely helium poor. Questions posedinclude: when does the atmosphere become chemically stratified and at whatrate?  The existence of several helium-rich subdwarfs suggests further questions;are there distinct subgroups of hot subdwarf, or do hot subdwarfs change theirsurface composition in the course of evolution? Recent analyses have revealedremarkable surface chemistries amongst the helium-rich subgroup. In this paper,we analyse high-resolution spectra of nine intermediate helium-rich hotsubdwarfs. We report the discovery that two stars, HE 2359-2844 and HE1256-2738, show an atmospheric abundance of lead which is nearly ten thousandtimes that seen in the Sun. This is measured from optical Pb IV absorptionlines never previously seen in any star. The lead abundance is ten to 100 timesthat measured in normal hot subdwarf atmospheres from ultraviolet spectroscopy.HE 2359-2844 also shows zirconium and yttrium abundances similar to those inthe zirconium star LS IV-14 116. The new discoveries are interpreted in termsof heavily stratified atmospheres and the general picture of a surfacechemistry in transition from a new-born helium-rich subdwarf to a normalhelium-poor subdwarf.

Discovery of extremely lead-rich subdwarfs: does heavy metal signal the formation of subdwarf B stars?