A team of astronomers from Taiwan and the UK has discovered two unusual subdwarf stars with extremely high concentrations of lead in their atmospheres.
According to their paper published in the journal Monthly Notices of the Royal Astronomical Society, these stars, labeled HE 2359-2844 and HE 1256-2738, have surfaces containing 10,000 times more lead than is present on the surface of the Sun.
HE 2359-2844 is a subdwarf located at a distance of 800 light-years away in the constellation of Sculptor.
The star HE 1256-2738 is located about 1,000 light years away in the constellation of Hydra.
The scientists using observations from the archives of the ESO’s Very Large Telescope in Chile identified a few features in spectra of both stars that did not match any atoms expected to be present. After some detective work, they realized that the features were due to lead.
Lead is one of the heaviest naturally occurring elements. In the Sun there is less than one lead atom for every ten billion hydrogen atoms.
At around 38,000 degrees Celsius, the surfaces of HE 2359-2844 and HE 1256-2738 are so hot that three electrons are removed from every lead atom. The resulting ions produce distinctive lines in the star’s spectrum, from which the concentration of lead in the atmosphere can be measured.
Using the same technique, HE 2359-2844 was also found to show ten thousand times more yttrium and zirconium than on the Sun.
Along with the zirconium star LS IV-14 116, the newly discovered stars form a new group of ‘heavy metal subdwarfs.’
Study lead author Dr Naslim Neelamkodan from Armagh Observatory and his colleagues explained that “the heavy-metal stars are a crucial link between bright red giants, stars thirty or forty times the size of the Sun, and faint blue subdwarfs, stars one fifth the size, but seven times hotter and seventy times brighter than the Sun.”
Bibliographic information: Naslim N et al. Discovery of extremely lead-rich subdwarfs: does heavy metal signal the formation of subdwarf B stars? MNRAS, published online July 25, 2013; doi: 10.1093/mnras/stt1091