C18O Depletion in Starless Cores in Taurus
  We present here findings for C18O depletion in eight starless cores in
Taurus: TMC-2, L1498, L1512, L1489, L1517B, L1521E, L1495A-S, and L1544. We
compare observations of the C18O J=2-1 transition taken with the ALMA prototype
receiver on the Heinrich Hertz Submillimeter Telescope to results of radiative
transfer modeling using RATRAN. We use temperature and density profiles
calculated from dust continuum radiative transfer models to model the C18O
emission. We present modeling of three cores, TMC-2, L1489, and L1495A-S, which
have not been modeled before and compare our results for the five cores with
published models. We find that all of the cores but one, L1521E, are
substantially depleted. We also find that varying the temperature profiles of
these model cores has a discernable effect, and varying the central density has
an even larger effect. We find no trends with depletion radius or depletion
fraction with the density or temperature of these cores, suggesting that the
physical structure alone is insufficient to fully constrain evolutionary state.
We are able to place tighter constraints on the radius at which C18O is
depleted than the absolute fraction of depletion. As the timeline of chemical
depletion depends sensitively on the fraction of depletion, this difficulty in
constraining depletion fraction makes comparison with other timescales, such as
the free-fall timescale, very difficult. Keywords: Stars:Formation --
ISM:abundances-- ISM:clouds -- Individual Objects: TMC-2, L1498, L1512, L1489,
L1517B, L1521E, L1495A-S, L1544
