#astronomy SALT 2019 – Astronotes
Mendacity someplace between younger main-sequence stars and outdated white dwarfs, sizzling subdwarfs are blue stars with about half the mass, a tenth the diameter and ten occasions the brightness of the Solar. They often have surfaces that are both extraordinarily hydrogen-rich or helium-rich. The previous are most likely on account of chemical diffusion within the
Mendacity someplace between younger main-sequence stars and outdated white dwarfs, sizzling subdwarfs are blue stars with about half the mass, a tenth the diameter and ten occasions the brightness of the Solar. They often have surfaces that are both extraordinarily hydrogen-rich or helium-rich. The previous are most likely on account of chemical diffusion within the stellar environment, which inspires the heavier helium to sink. The latter are most likely on account of earlier evolution, probably the merger of two white dwarfs, which has led to the destruction of hydrogen.
In between, is a small group of stars with intermediate helium abundances — that’s between 20 and 80% helium. In recent times, many of those have been found to indicate outstanding overabundances of sure iron-group and/or trans-iron components, together with zirconium and lead. The frequency with which these stars happen, the vary of floor properties, and the rationale for his or her extraordinary floor traits symbolize vital questions for subdwarf astronomy.
Over the previous three years, Simon Jeffery (AOP) and Brent Miszalski (SALT) have been conducting a medium- and high-resolution spectroscopic survey of southern sizzling subdwarfs with the Southern African Giant Telescope. They’ve found many uncommon stars, of which EC 22536−5304 was the primary SALT ‘heavy-metal’ subdwarf.
SALT spectra present sturdy absorption traces of triply ionized lead. The HRS spectrum and a follow-up SALT/RSS spectrum present EC 22536−5304 to have floor properties (temperature, gravity, helium/hydrogen ratio) much like different heavy-metal subdwarfs. With lead within the star’s atmospheres being almost 100,000 occasions extra abundance that within the Solar, EC 22536−5304 is essentially the most lead-rich intermediate helium subdwarf found up to now. The environment is reasonably wealthy in carbon and oxygen, with the abundances of each exceeding that of nitrogen. Analyses of EC 22536−5304 and different heavy-metal subdwarfs with SALT and different telescope are ongoing. These purpose to grasp bodily processes resembling atomic diffusion at present at work in the stellar environment, in addition to the star’s historical past which led to the decreased hydrogen abundance.
A part of the SALT/RSS spectrum of EC 22536−5304 (black) displaying the places of two traces of triply ionised lead. The road at 4049A is clearly seen; Neither PbIV line is current within the mannequin used on this determine (purple). Different outstanding traces are additionally labelled.
Article by: Prof. Simon Jeffery, Armagh Observatory and Planetarium