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The first stars are unique not only in being first but also because of
being first, they have a unique and pristine primordial initial
composition, which can dramatically alter both their evolution, the
way they die as supernovae, and their resulting nucleosynthesis. For
example, the recently discovered most iron-poor star known,
SM0313-6708, hints at some primordial production process of calcium
that can only be found and seen in such pristine stars. Another
example is that reduced mass loss and higher characteristic initial
masses may lead to a population of pair instability supernovae that
could produce a very unique abundance pattern.
No direct observations of these stars are possible at this time,
however, so our ability to study these early stars is limited to
indirect measurements and numerical simulations, though possibly we
might be able to observe some of their stellar deaths in the near
future. Stellar forensics based on nucleosynthesis patterns preserved
in subsequent generations of stars may be used to attempt
reconstruction of the properties of these first stars. But in order
to be able to use this tool, we need know what abundances were
synthesised in these first generations of stars.
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