  (Aims) Near-infrared imaging polarimetry at high-angular resolutions has
revealed intriguing distribution of circumstellar dust towards FU Ori-type
objects (FUors). These dust grains are probably associated with either an
accretion disk or an infalling envelope. Follow-up observations in the
mid-infrared would lead us to a better understanding of the hierarchy of the
mass accretion processes onto FUors (i.e., envelope and disk accretion), which
hold keys for understanding the mechanism of their accretion outbursts and the
growth of low-mass young stellar objects in general. (Method) We have developed
a semi-analytic method to estimate the mid-infrared intensity distributions
using the observed polarized intensity (PI) distributions in H-band
(lambda=1.65 micron). We have derived intensity distributions for two FUors, FU
Ori and V1735 Cyg, at three wavelengths (lambda=3.5/4.8/12 micron) for various
cases, i.e. with a star or a flat compact self-luminous disk as an illuminating
source; an optically thick disk or an optically thin envelope for circumstellar
dust grains; and three different dust models. (Results) We have been able to
obtain self-consistent results for many cases and regions, in particular when
the viewing angle of the disk/envelope is zero (face-on). Our calculations
suggest that the mid-infrared extended emission at the above wavelengths is
dominated by the single scattering process. The contribution of thermal
emission is negligible unless we add an additional heating mechanism such as
adiabatic heating in spiral structures and/or fragments. The uncertain nature
of the central illuminating source, the distribution of circumstellar dust
grains and the optical properties of dust grains yield uncertainties in the
intensity levels on orders of magnitude, e.g., 20-800, for the disk/envelope
aspect ratios of ~0.2 and lambda=3-13 micron.
