THE DISTRIBUTION OF DUST CLOUDS IN THE INTERSTELLAR-MEDIUM

Murthy, Walker, & Henry (1992) examined 745 O, B, F and G stars on the IRAS Skyflux plates in a search for dust clouds that are heated by th e stars and found 123 clouds near 106 stars by detection of excess 60 mu m emission. We have reanalyzed their sample using the Infrared Sky Survey Atlas (ISSA) data and found 194 clouds near 138 stars. We find a filling factor of (0.02 +/- 0.01) for dust of density greater than s imilar to 3.0 H atoms cm(-3) to which we are complete. We were able to find a good model fit to the data set with these parameters for the d ust clouds: filling factor = 0.085 +/- 0.03, scale height z = 250 +/- 100 pc, radius power-law exponent alpha = -4.26 +/- 0.25, and density power-law exponent beta = -1.15 +/- 0.1, where the filling factor incl udes material in the density range 0.01-100 H atoms cm(-3); however, t here is evidence to suggest that the region probed by these stars is a special environment. We also find significantly lower dust densities near O stars than near B stars.