Evidence for Population III Stars ~ Tony Baxter
Stars observed in galaxies were originally divided into two populations by Walter Baade in the 1940s. Although a more refined means of classifying stellar populations has since been established (according to whether they are found in the thin disk, thick disk, halo or bulge of the galaxy), astronomers have continued to coarsely classify stars as either Population I (Pop I, metal-rich) or Population II (Pop II, metal-poor). However, even the most metal-poor Pop II stars have metallicities (commonly denoted [Z/H]) far above that of the gas left over from the Big Bang.
For this reason, astronomers have introduced a third class of star. Population III (Pop III) stars are composed entirely of primordial gas – hydrogen, helium and very small amounts of lithium and beryllium. This means that the gas from which Pop III stars formed had not been ‘recycled’ (incorporated into, and then expelled) from previous generations of stars, but was pristine material left over from the Big Bang. As such, these stars would have a [Z/H] ~ -10 and would constitute the very first generation of stars formed within a galaxy. These Pop III stars would then produce the metals observed in Pop II stars and initiate the gradual increase in metallicity across subsequent generations of stars.
The only problem is that Pop III stars are hypothetical. Despite intense searches, no Pop III star had ever been observed, that is until this year with the discovery of CR7. Tony will present the latest findings in this area of research
Atomic Clocks: The celebration, the how and the where.~ David Hornsby
Celebrating 60 years since the world's first successful atomic clock was demonstrated at the NPL.
How do atomic clocks actually work?
Where are atomic clocks mainly used?
What are Lagrangian points? ~ Roger Wood
The Lagrangian points are positions in the orbital configuration of two large bodies where a small object affected only by gravity can maintain a stable position relative to the two large bodies ... There are five such points, labeled L1 to L5, all in the orbital plane of the two large bodies.
How does this come about? Where are they in the Solar System? How have space scientists exploited them, and how might they be further exploited in the future?"