New Optical Reddening Maps of the Large and Small Magellanic Clouds
  We present new reddening maps of the SMC and LMC based on the data of the
third phase of the Optical Gravitational Lensing Experiment (OGLE III). We have
used two different methods to derive optical reddening maps. We adopt a
theoretical mean unreddened colour for the red clump in the SMC and LMC,
respectively. We subdivide the photometric data for both Clouds into subfields
and calculate the difference between the observed red clump position and the
theoretical value for each field, which provides us with the reddening value in
(V-I). Furthermore reddening values are obtained for 13490 LMC RR Lyrae ab and
1529 SMC RR Lyrae ab stars covering the whole OGLE III region of the MCs. The
observed colours (V-I) of the RR Lyrae stars are compared with the colour from
the absolute magnitudes. The absolute magnitude of each RR Lyrae star is
computed using its period and metallicity derived from Fourier decomposition of
its lightcurve. In general we find a low and uniform reddening distribution in
both Magellanic Clouds. The red clump method indicates a mean reddening of the
LMC of E(V-I) = 0.09 +/- 0.07 mag, while for the SMC E(V-I) = 0.04 +/- 0.06 mag
is obtained. With RR Lyrae stars a median value of E(V-I) = 0.11 +/- 0.06 mag
for the LMC and E(V-I) = 0.07 +/- 0.06 mag for the SMC is found. The LMC shows
very low reddening in the bar region, whereas the reddening in the star-forming
leading edge and 30 Doradus is considerably higher. In the SMC three pronounced
regions with higher reddening are visible. Two are located along the bar, while
the highest reddening is found in the star-forming wing of the SMC. In general
the regions with higher reddening are in good spatial agreement with infrared
reddening maps as well as with reddening estimations of other studies. The
position-dependent reddening values from the red clump method are available via
the Virtual Observatory interface.
