摘要：Context. The mass of prestellar cores is an essential ingredient to
understand the onset of star formation in the core. The low level of emission from cold
dust may keep parts of this dust hidden from observation.
Aims. We aim to determine the fraction of core mass in the temperature
range <8 K that can be
expected for typical low- and high-mass star formation regions.
Methods. We calculated the dust temperature within standard spherically
symmetric prestellar cores for a grid of density power laws in the outer core regions,
core masses, and variations in the external multicomponent radiation field. We assume the
dust is composed of amorphous silicate and carbon and we discuss variations of its optical
properties. As a measure for the distribution of cores and clumps, we used core mass
functions derived for various environments. In view of the high densities in very cold
central regions, dust and gas temperatures are assumed to be equal.
Results. We find that the fraction of mass with temperatures
<8 K in typical low- and
high-mass cores is <20%. It
is possible to obtain higher fractions of very cold gas by placing intermediate- or
high-mass cores in a typical low-mass star formation environment. We show that the mass
uncertainty arising from far-infrared to mm modeling of very cold dust emission is smaller
than the mass uncertainty owing to the unknown dust opacities.
Conclusions. Under typical star formation conditions, dust with
temperatures <8 K covers a
small mass fraction in molecular cloud cores, but may play a more important role for
special cases. The major unknown in determining the total core mass from thermal dust
emission is the uncertainty in the dust opacity, not in the underestimated very cold dust
mass.
