On The Gas Temperature of Molecular Cloud Cores
  We investigate the uncertainties affecting the temperature profiles of dense
cores of interstellar clouds. In regions shielded from external ultraviolet
radiation, the problem is reduced to the balance between cosmic ray heating,
line cooling, and the coupling between gas and dust. We show that variations in
the gas phase abundances, the grain size distribution, and the velocity field
can each change the predicted core temperatures by one or two degrees. We
emphasize the role of non-local radiative transfer effects that often are not
taken into account, for example, when modelling the core chemistry. These
include the radiative coupling between regions of different temperature and the
enhanced line cooling near the cloud surface. The uncertainty of the
temperature profiles does not necessarily translate to a significant error in
the column density derived from observations. However, depletion processes are
very temperature sensitive and a two degree difference can mean that a given
molecule no longer traces the physical conditions in the core centre.
