Prestellar core modeling in the presence of a filament - The dense heart
  of L1689B
  Short version: We apply a new synergetic radiative transfer method: the
derived 1D density profiles are both consistent with a cut through the Herschel
PACS/SPIRE and JCMT SCUBA-2 continuum maps of L1689B and with a derived local
interstellar radiation field. Choosing an appropriate cut along the filament
major axis, we minimize the impact of the filament emission on the modeling.
For the bulk of the core (5000-20000 au) an isothermal sphere model with a
temperature of around 10 K provides the best fits. We show that the power law
index of the density profile, as well as the constant temperature can be
derived directly from the radial surface brightness profiles. For the inner
region (< 5000 au), we find a range of densities and temperatures that are
consistent with the surface brightness profiles and the local interstellar
radiation field. Based on our core models, we find that pixel-by-pixel single
temperature spectral energy distribution fits are incapable of determining
dense core properties. We conclude that, to derive physical core properties, it
is important to avoid an azimuthal average of core and filament.
Correspondingly, derived core masses are too high since they include some mass
of the filament, and might introduce errors when determining core mass
functions. The forward radiative transfer methods also avoids the loss of
information owing to smearing of all maps to the coarsest spatial resolution.
We find the central core region to be colder and denser than estimated in
recent inverse radiative transfer modeling, possibly indicating the start of
star formation in L1689B.
