Molecular Outflows Driven by Low-Mass Protostars. I. Correcting for
  Underestimates When Measuring Outflow Masses and Dynamical Properties
  We present a survey of 28 molecular outflows driven by low-mass protostars,
all of which are sufficiently isolated spatially and/or kinematically to fully
separate into individual outflows. Using a combination of new and archival data
from several single-dish telescopes, 17 outflows are mapped in CO (2-1) and 17
are mapped in CO (3-2), with 6 mapped in both transitions. For each outflow, we
calculate and tabulate the mass, momentum, kinetic energy, mechanical
luminosity, and force assuming optically thin emission in LTE at an excitation
temperature of 50 K. We show that all of the calculated properties are
underestimated when calculated under these assumptions. Taken together, the
effects of opacity, outflow emission at low velocities confused with ambient
cloud emission, and emission below the sensitivities of the observations
increase outflow masses and dynamical properties by an order of magnitude, on
average, and factors of 50-90 in the most extreme cases. Different (and
non-uniform) excitation temperatures, inclination effects, and dissociation of
molecular gas will all work to further increase outflow properties. Molecular
outflows are thus almost certainly more massive and energetic than commonly
reported. Additionally, outflow properties are lower, on average, by almost an
order of magnitude when calculated from the CO (3-2) maps compared to the CO
(2-1) maps, even after accounting for different opacities, map sensitivities,
and possible excitation temperature variations. It has recently been argued in
the literature that the CO (3-2) line is subthermally excited in outflows, and
our results support this finding.
