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

extending our simulation to later times might show that the most massive star
would ultimately have to compete with its secondary companion for mass. As
pointed out in Turk et al. (2009), if this in the end prevents the largest star
from reaching very high masses (> ∼ 100 M⊙), this would also affect its resulting
chemical signature. If multiple star formation were common in Pop III, then
the occurrence of pair-instability supernovae (PISNe) might be significantly
reduced, since stars that explode as PISNe must be in the higher mass range
(140 M⊙ < M∗ < 260 M⊙, Heger and Woosley 2002). Extremely metal-poor
Galactic halo stars are believed to preserve the nucleosynthetic pattern of the
first SNe, so this may help to explain the lack of PISNe chemical signatures
found in halo stars (e.g. Christlieb et al. 2002; Beers and Christlieb 2005;
Frebel et al. 2005; Tumlinson 2006; Karlsson et al. 2008). Turk et al. (2009)
also note that if multiple high-mass Pop III stars can form within a minihalo
at similar times, the ionizing flux on neighboring minihalos could be increased,
possibly leading to more efficient molecular cooling and ultimately lower-mass
(Pop III.2) stars in the neighboring halos (e.g. O’Shea et al. 2005). This again
would influence the chemical signature of extremely metal-poor Galactic halo
stars.
It should be mentioned that tight binaries on scales smaller than the
resolution of our simulation could also form. Though a higher resolution study
would be necessary to confirm this, the formation of a fragmenting disk of
steadily increasing angular momentum in our cosmological simulation makes
this a reasonable possibility. This could also limit the mass of Pop III stars,
yielding similar effects on their resulting chemical signature as discussed above.
The possible binary nature of Pop III stars, provided that they would not grow
to become very massive, may also yield a direct primordial formation pathway
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