Dust properties of nearby disks: M31 case
  Several properties of the M31 disk, namely: opacity, extinction law and
gas-to-dust ratio are studied by means of optical and near-infrared photometry
of ten globular clusters and galaxies seen through the disk. The individual
extinctions of these objects were estimated with respect to several sets of
theoretical spectral energy distributions for globulars and galaxies. Seven
targets are consistent with reddened globulars, two - with starburst galaxies
and one - with an elliptical. The extinction estimates agree with
semi-transparent disk (Av ~ 1) in the inter-arm regions. The total-to-selective
extinction ratio in those regions 2.75 is lower on average than the typical
Galactic value of Rv=3.1. We also obtained a gas-to-dust ratio, similar to that
in the the Milky way. It shows no correlation with the distance from the M31
center.
