Optical Properties of Interstellar Dust around the Orion A Molecular
  Cloud
  We have studied optical properties of interstellar dust around the Orion A
molecular cloud to investigate the size distribution and the composition of
dust grains. Orion A is one of the most studied molecular clouds in the solar
vicinity ($d \simeq 400\ \rm{pc}$). In this paper, we used optical and
near-infrared photometric data. The optical data were obtained by $BVRI$ bands
imaging observations. The near-infrared data consisting of $JHK_{S}$ bands were
taken from 2MASS point source catalog. We produced some color excess maps
around Orion A, and measured their ratios such as $E(R-I)/E(B-V)$. In order to
investigate dust properties, we compared the observed ratios with results of
simulation performed by Naoi T. et al. (2021) who calculated the extinction in
the optical to near-infrared wavelengths based on a standard dust model; they
assumed a power-law grain-size distribution with an upper cutoff radius and
assumed $graphite$ and $silicate$ as dominant components. As a result, we found
that the upper cutoff radius around Orion A is $\simeq 0.3$ $\rm{\mu}$m, and
$silicate$ predominates compared with $graphite$ (with the fraction of
$silicate$ grater than $93$ %). In addition, we further derived the
total-to-selective extinction ratio $R_{V}$ from the observed extinction of
$A_{V}$ and the color excess $E(B-V)$, and compared it with the model
calculations. Dust properties (i.e., the upper cutoff radius and the ratio of
$graphite/silicate$) derived from $R_{V}$ is almost consistent with those
derived from the color excess ratios.
