Lead star

A lead star is a low-metallicity star with an overabundance of the elements lead and bismuth as compared to other products of the S-process.^[1] Many of these lead stars have more lead in them than all other elements heavier than iron.^{[clarification needed]} The amount of lead in each of these stars is roughly the mass of the Moon.^[2] This type of star confirms predictions about the abundances of elements above iron in AGB stars.^[3]

It is theorised that lead is produced in AGB stars by the s-process, the capture of neutrons to produce progressively-heavier elements. The neutrons in AGB stars are produced primarily by the collision of carbon and helium nuclei, producing an oxygen nucleus and a neutron. The process is slow, with decades passing between the capture of each neutron in a nucleus, but in low-metallicity stars, the neutrons are all captured by the relatively few high-mass nuclei in their atmospheres. This leads to most heavy elements being converted to the highest stable mass, which is generally lead; as more lead is produced, the other heavy elements become depleted.^[2]

Several stars have been confirmed to be lead stars. Among them are HD 187861, HD 196944 and HD 224959.^[3] In one study, nine stars were detected with high lead abundances and most of them were carbon-enhanced metal-poor stars (CEMP stars).^[4] There was also the discovery of two hot subdwarf stars named HE 2359−2844 and HE 1256−2738. Both of these stars had lead abundances nearly 10,000 times that of the Sun in their atmospheres.^[5]