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

N. Naslim, C. S. Jeffery, A. Hibbert, N. T. Behara

Research output: Contribution to journalArticlepeer-review

52 Citations (Scopus)


Hot subdwarfs represent a group of low-mass helium-burning stars formed through binarystar 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, showan atmospheric abundance of lead which is nearly 10 000 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 10 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.

Original languageEnglish
Pages (from-to)1920-1929
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - Sept 2013
Externally publishedYes


  • Atomic data
  • Stars: abundances
  • Stars: chemically peculiar
  • Stars: evolution
  • Stars: horizontal branch
  • Subdwarfs

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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