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

ate found at late times in our ‘no-feedback case’ as well as the simulations
of, e.g., Greif et al. (2011); Smith et al. (2011). This model well-matches the
prescription used in the simulation, particularly in effective temperature and
ionizing luminosity, and both predict that ionizing radiation will exceed the
influx of neutral particles, and that break-out beyond the sink occurs at < ∼
1000 yr. Though the protostar most likely does not reach the ZAMS within
the time of our simulation, our simple model serves as a reasonable approxi-
mation for any unresolved accretion luminosity. We also note that Hosokawa
et al. (2010) find that, for a given accretion rate, primordial protostars under-
going disk accretion will have considerably smaller radii than those accreting
mass in a spherical geometry. The rapid contraction of the protostar between
500 and 1000 years therefore serves as an idealized representation of the sub-
sink material evolving from a spherical to a disk geometry as it gains angular
momentum.
As discussed in Smith et al. (2011), the sink particle method requires
several simplifying assumptions when constructing the protostellar model. By
setting the protostellar mass equal to the sink mass, we are assuming that
the small-scale disk which likely exists within the sink region has low mass
compared to the protostar. We also assume that the accretion rate at the sink
edge is the same as the accretion rate onto the star, when in reality after gas
enters within racc it must likely be processed through a small-scale disk before
being incorporated onto the star. However, our assumption may still be a good
approximation of physical reality, given that the primordial protostellar disk
study of Clark et al. (2011b) implies that the thin disk approximation would
probably not be valid on sub-sink scales (e.g. Pringle 1981), and that strong
gravitational torques can quickly drive mass onto the star. Furthermore, as
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