Multi-wavelength observations and modelling of a quiescent cloud LDN1512
  Light scattering at near-infrared wavelengths has been used to study the
optical properties of the interstellar dust grains, but these studies are
limited by the assumptions on the strength of the radiation field. On the other
hand, thermal dust emission can be used to constrain the properties of the
radiation field, although this is hampered by uncertainty about the dust
emissivity. We test if current dust models allow us to model a molecular cloud
simultaneously in the near infrared (NIR) and far infrared (FIR) wavelengths
and compare the results with observations. Our aim is to place constraints on
the properties of the dust grains and the strength of the radiation field. We
present computations of dust emission and scattered light of a quiescent
molecular cloud LDN1512. We construct radiative transfer models for LDN1512
that include an anisotropic radiation field and a three-dimensional cloud
model. We are able to reproduce the observed FIR observations, with a radiation
field derived from the DIRBE observations, with all of the tested dust models.
However, with the same density distribution and the assumed radiation field,
the models fail to reproduce the observed NIR scattering in all cases except
for models that take into account dust evolution via coagulation and mantle
formation. We find that the column densities derived from our radiative
transfer modelling can differ by a factor of up to two, compared to the column
densities derived from the observations with modified blackbody fits. The
discrepancy in the column densities is likely caused because of temperature
difference between a modified blackbody fit and the real spectra.
  We show that the observed dust emission can be reproduced with several
different assumptions about the properties of the dust grains. However, in
order to reproduce the observed scattered surface brightness dust evolution
must be taken into account.
