Attenuation Caused by a Distant Isothermal Turbulent Screen

We analyse in detail the attenuation caused by an isothermal turbulentdistant foreground dust screen. The attenuation curve is well determined by twoparameters, the absolute-to-relative attenuation ratio R^A_V=A_V/E(B-V) and theabsolute attenuation A_V. We show quantitatively how these two observablequantities depend on the statistical properties of the local density and themean attenuation and how they vary with the thickness of the screenmeasured in units of the largest turbulent scale. The attenuation through aturbulent medium is characterised by higher transparency and a flatterattenuation curve in comparison with a homogeneous dust screen. In general, theeffect of the turbulent medium on the attenuation increases with slicethickness. In the limit of thick slices, typically larger than the maximumturbulent scale, R^A_V asymptotically approaches a maximum value.Comment: 38 pages, 48 figures, accepted for publication in ApJ, Jan. 200