Extinction in the Large Magellanic Cloud Bar around NGC1854, NGC1856,
  and NGC1858
  We report on the extinction properties in the fields around the clusters NGC
1854, NGC 1856, and NGC 1858 in the bar of the Large Magellanic Cloud. The
colour-magnitude diagrams of the stars in all these regions show an elongated
red giant clump that reveals a variable amount of extinction across these
fields, ranging from Av~0.2 to Av~1.9, including Galactic foreground
extinction. The extinction properties nonetheless are remarkably uniform. The
slope of the reddening vectors measured in the (V-I,V) and (B-I,B)
colour-magnitude planes is fully in line with the Av/E(B-V)~5.5 value found in
the outskirts of 30 Dor. This indicates the presence of an additional grey
extinction component in the optical requiring big grains to be about twice as
abundant as in the diffuse Galactic interstellar medium (ISM). Areas of higher
extinction appear to be systematically associated with regions of more intense
star formation, as measured by the larger number of stars more massive than 8
Msun, thus making injection of big grains into the ISM by SNII explosion the
likely mechanism at the origin of the observed grey extinction component.
