15$\%$ on average for sufficiently high *E*(*B-V*) as much as 0.02. The optical depth at 1565 [Å]{} was derived from *E*(*B-V*) assuming R$_V$ to be = 3.1, an average value of the diffuse ISM, with the absorption coefficients calculated for the carbonaceous-silicate grains model [@wei01]. In fact, we estimated the average R$_V$ value for the OES region using the values made for the 6 OES stars in @lar05 and the A$_V$ values provided by @nec80 for the 11 OES stars with *E*(*B-V*) &gt; 0.05, and obtained 3.2, which was very close to the average value of the diffuse ISM. Furthermore, the extinction curves for five OES stars (HD23466, 24263, 26912, 30076, and 30870) in @pap91 are more or less consistent with R$_V$=3.1.

The most serious difficulty with the present simulation is related to the dust distribution since there is no report regarding the spatial distribution of dust for the OES region, other than the infrared survey results that give only indirect information on the integrated amount of dust along the sightlines. Hence, we assumed the dust cloud to be a slab of finite thickness for the sake of convenience. This idealized dust model may certainly be different from the real 