Variation of the Core Lifetime and Fragmentation Scale in Molecular
  Clouds as an Indication of Ambipolar Diffusion
  Ambipolar diffusion likely plays a pivotal role in the formation and
evolution of dense cores in weakly-ionized molecular clouds. Linear analyses
show that the evolutionary times and fragmentation scales are significantly
greater than the hydrodynamic (Jeans) values even for clouds with mildly
supercritical mass-to-flux ratio. We utilize values of fragmentation scales and
growth times that correspond to typical ionization fractions within a molecular
cloud, and apply to the context of the observed estimated lifetime of
prestellar cores as well as the observed number of such embedded cores forming
in a parent clump. By varying a single parameter, the mass-to-flux ratio, over
the range of observationally measured densities, we fit the range of estimated
prestellar core lifetimes ($\sim 0.1$ to a few Myr) identified with Herschel as
well as the number of embedded cores formed in a parent clump measured in
Perseus with the Submillimeter Array (SMA). Our model suggests that the
prestellar cores are formed with a transcritical mass-to-flux ratio and higher
densities correspond to somewhat higher mass-to-flux ratio but the normalized
mass-to-flux ratio $\mu$ remains in the range $1 \lesssim \mu \lesssim 2$. Our
best-fit model exhibits $B \propto n^{0.43}$ for prestellar cores, due to
partial flux-freezing as a consequence of ambipolar diffusion.
