A Systematic Study of the dust of Galactic Supernova Remnants I. The
  Distance and the Extinction
  By combining the photometric, spectroscopic, and astrometric information of
the stars in the sightline of SNRs, the distances to and the extinctions of 32
Galactic supernova remnants (SNRs) are investigated. The stellar atmospheric
parameters are from the SDSS$-$DR14$/$APOGEE and LAMOST$-$DR5$/$LEGUE
spectroscopic surveys. The multi-band photometry, from optical to infrared, are
collected from the {\it Gaia}, APASS, Pan--STARRS1, 2MASS, and {\it WISE}
surveys. With the calibrated {\it Gaia} distances of individual stars, the
distances to 15 of 32 SNRs are well determined from their produced extinction
and association with molecular clouds. The upper limits of distance are derived
for 3 SNRs. The color excess ratios $E(g_{\rm P1}-\lambda) / E(g_{\rm
P1}-r_{\rm P1})$ of 32 SNRs are calculated, and their variation with wavebands
is fitted by a simple dust model. The inferred dust grain size distribution
bifurcates: while the graphite grains have comparable size to the average ISM
dust, the silicate grains are generally larger. Along the way, the average
extinction law from optical to near-infrared of the Milky Way is derived from
the 1.3 million star sample and found to agree with the CCM89 law with $R_{\rm
V}=3.15$.
