Subluminous B stars come in a variety of flavours including single stars , close and wide binaries , and pulsating and non-pulsating variables .
A majority have helium-poor surfaces ( helium by number n _ { He } < 1 \% ) , whilst a minority have extremely helium-rich surfaces ( n _ { He } > 90 \% ) .
A small number have an intermediate surface helium abundance ( \approx 10 - 30 \% ) , accompanied by peculiar abundances of other elements .
The questions posed are i ) whether these abundance peculiarities are associated with radiatively-driven and time-dependent stratification of elements within the photosphere as the star evolves from an helium-enriched progenitor to become a normal helium-poor sdB star , and ii ) whether these phenomena occur only in single sdB stars or are also associated with sdB stars in binaries .

We present a fine analysis of the bright intermediate-helium sdB star CPD -20 ^ { \circ } 1123 ( Albus 1 ) which shows it to be cool , for a hot subdwarf , with T _ { eff } \approx 23 000 K and with a surface helium abundance \approx 17 \% by number .
Other elements do not show extraordinary anomalies ; in common with majority sdB stars , carbon and oxygen are substantially depleted , whilst nitrogen is enriched .
Magnesium through sulphur appear to be depleted by \approx 0.5 dex , but chlorine and argon are substantially enhanced .

We also present a series of radial-velocity measurements which show the star to be a close binary with an orbital period of 2.3 d , suggesting it to be a post-common-envelope system .

The discovery of an intermediate helium-rich sdB star in a close binary in addition to known and apparently single exemplars supports the view that these are very young sdB stars in which radiatively-driven stratification of the photosphere is incomplete .