We report on an investigation into stellar evolution and nucleosynthesis in the low and extremely low metallicity regime , including models of stars with a pure Big Bang composition ( i.e . Z = 0 ) .
The metallicity range of the extremely metal-poor ( EMP ) models we have calculated is -6.5 < \textrm { [ Fe / H ] } < -3.0 , whilst our models are in the mass range 0.85 < \textrm { M } < 3.0 \textrm { M } _ { \odot } .
Many of the EMP and Z = 0 models experience violent evolutionary episodes not seen at higher metallicities .
We refer to these events as ‘ Dual Flashes ’ since they are characterised by peaks in the hydrogen and helium burning luminosities occurring at roughly the same time .
Some of the material processed by these events is later dredged up by the convective envelope , causing significant surface pollution .
These events have been reported by previous studies , so our results reaffirm their occurrence – at least in 1D stellar models .
The novelty of this study is that we have calculated the entire evolution of the Z = 0 and EMP models , from the ZAMS to the end of the TPAGB , including detailed nucleosynthesis .
We have also calculated the nucleosynthetic yields , which will soon be available in electronic format .
Although subject to many uncertainties these are , as far as we are aware , the only yields available in this mass and metallicity range .
In this paper we briefly describe some of the results in the context of abundance observations of EMP halo stars .
This work formed part of SWC ’ s PhD thesis ( completed in March 2007 ) and a series of subsequent papers will describe the results of the study in more detail .