Copyright by Athena Ranice Stacy 2011 - The University of Texas at ...

small multiple system forms, dominated by a binary with masses ∼ 40 M⊙ and
∼ 10 M⊙. If Pop III stars were to form typically in binaries or small multiples,
this would have crucial consequences for the observational signature of the
first stars, such as the nucleosynthetic pattern of the SNe they produce, and
the gravitational-wave emission from possible Pop III black-hole binaries.
In Chapter 3, we examined the growth of metal-free, Pop III stars
under radiative feedback. Using the sink particle method within a cosmological
simulation, we modeled the effect of LW radiation emitted by the protostar,
and employed a ray-tracing scheme to follow the growth of the surrounding
H ii region. We again find that a disk assembles around the first protostar,
and that radiative feedback will not prevent further fragmentation of the disk
to form multiple Pop III stars. The resuling heating and ionization of the
gas leads to a shutoff of accretion once the main sink has grown to 15 M⊙
while the second sink has grown to 5 M⊙. There is little further accretion
or fragmentation afterwards, indicating the most likely outcome is a massive
Pop III binary. If Pop III stars were typically unable to grow to more than
a few tens of solar masses, this would have important consequences for the
occurence of pair-instability supernovae in the early universe as well as the
Pop III chemical signature in the oldest stars observable today.
In Chapter 4 we employed a cosmological simulation to estimate the
rotation speed of Pop III stars within a minihalo. Again using sink particles,
we measured the velocities and angular momenta of all particles that fall onto
these protostellar regions. This allowed us to record the angular momentum of
the sinks and estimate the rotational velocity of the Pop III stars expected to
form within them. We find that there is sufficient angular momentum to yield
rapidly rotating stars (> ∼ 1000 km s −1 , or near break-up speeds). This indicates
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