摘要：Context. Stars form by the gravitational collapse of cold and dense
molecular cloud cores. Constraining the temperature and density structure of such cores is
fundamental for understanding the initial conditions of star formation. We use
Herschel observations of the thermal far-infrared (FIR) dust emission
from nearby and isolated molecular cloud cores and combine them with ground-based
submillimeter continuum data to derive observational constraints on their temperature and
density structure.
Aims. The aim of this study is to verify the validity of a ray-tracing
inversion technique developed to derive the dust temperature and density structure of
nearby and isolated starless cores directly from the dust emission maps and to test if the
resulting temperature and density profiles are consistent with physical models.
Methods. We have developed a ray-tracing inversion technique that can be
used to derive the temperature and density structure of starless cores directly from the
observed dust emission maps without the need to make assumptions about the physical
conditions. Using this ray-tracing inversion technique, we derive the dust temperature and
density structure of six isolated starless molecular cloud cores from dust emission maps
in the wavelengths range 100 μm–1.2 mm. We then employ self-consistent radiative
transfer modeling to the density profiles derived with the ray-tracing inversion method.
In this model, the interstellar radiation field (ISRF) is the only heating source. The
local strength of the ISRF as well as the total extinction provided by the outer envelope
are treated as semi-free parameters which we scale within defined limits. The best-fit
values of both parameters are derived by comparing the self-consistently calculated
temperature profiles with those derived by the ray-tracing method.
Results. We confirm earlier results and show that all starless cores are
significantly colder inside than outside, with central core temperatures in the range
7.5−11.9 K and envelope
temperatures that are 2.4 −
9.6 K higher. The core temperatures show a strong negative correlation
with peak column density which suggests that the thermal structure of the cores is
dominated by external heating from the ISRF and shielding by dusty envelopes. We find that
temperature profiles derived with the ray-tracing inversion method can be well-reproduced
with self-consistent radiative transfer models if the cores have geometry that is not too
complex and good data coverage with spatially resolved maps at five or more wavelengths in
range between 100 μm and 1.2 mm. We also confirm results from earlier
studies that found that the usually adopted canonical value of the total strength of the
ISRF in the solar neighbourhood is incompatible with the most widely used dust opacity
models for dense cores. However, with the data available for this study, we cannot
uniquely resolve the degeneracy between dust opacity law and strength of the ISRF.
关键词：stars: formation;stars: low-mass;ISM: clouds;ISM: structure;dust, extinction;infrared: ISM
