  The discovery of supernovae associated with long-duration gamma ray burst
observations is primary evidence that the progenitors of these outbursts are
massive stars. One of the principle mysteries in understanding these
progenitors has been the fact that all of these gamma-ray burst associated
supernovae are type Ic supernovae, with no evidence of helium in the stellar
atmosphere. Many studies have focused on whether or not this helium is simply
hidden from spectral analyses. In this paper, we show results from recent
stellar models using new convection algorithms based on our current
understanding of stellar mixing. We demonstrate that enhanced convection may
lead to severe depletion of stellar helium layers, suggesting that the helium
is not observed simply because it is not in the star. We also present
light-curves and spectra of these compact helium-depleted stars, compared to
models with more conventional helium layers.
