Parameterizing the interstellar dust temperature
  The temperature of interstellar dust particles is of great importance to
astronomers. It plays a crucial role in the thermodynamics of interstellar
clouds, because of the gas-dust collisional coupling. It is also a key
parameter in astrochemical studies that governs the rate at which molecules
form on dust. In 3D (magneto)hydrodynamic simulations often a simple expression
for the dust temperature is adopted, because of computational constraints,
while astrochemical modelers tend to keep the dust temperature constant over a
large range of parameter space. Our aim is to provide an easy-to-use parametric
expression for the dust temperature as a function of visual extinction ($A_{\rm
V}$) and to shed light on the critical dependencies of the dust temperature on
the grain composition. We obtain an expression for the dust temperature by
semi-analytically solving the dust thermal balance for different types of
grains and compare to a collection of recent observational measurements. We
also explore the effect of ices on the dust temperature. Our results show that
a mixed carbonaceous-silicate type dust with a high carbon volume fraction
matches the observations best. We find that ice formation allows the dust to be
warmer by up to 15% at high optical depths ($A_{\rm V}> 20$ mag) in the
interstellar medium. Our parametric expression for the dust temperature is
presented as $T_{\rm d} = \left[ 11 + 5.7\times \tanh\bigl( 0.61 -
\log_{10}(A_{\rm V})\bigr) \right] \, \chi_{\rm uv}^{1/5.9}$, where $\chi_{\rm
uv}$ is in units of the Draine (1978) UV field
