Session 15 - Interstellar Medium I.
Display session, Monday, January 15
North Banquet Hall, Convention Center

## [15.01] The Longitudinal Dependence of the IRAS I_60\mum - I_100\mum Flux Density Ratio

D. R. Ciardi, R. W. Canterna (U. Wyoming/WIRO)

We present a study of the diffuse infrared emission of the Galaxy for the region 42^\circ \leq l \leq 146^\circ and 10^\circ \leq b \leq 50^\circ. The study was performed using the IRAS Sky Survey Atlas at 60\mum and 100\mum. The mean I_60\mum - I_100\mum flux density ratio is found to be 0.173 (0.001). However, the flux density ratio as a function of longitude deviates from the mean by an average of 18%. The flux density ratios have been translated into a minimum particle size for the dust, and it is found that the minimum particle size varies by a factor of ten (0.0003 - 0.003\mum). The maximum flux density ratio is found to be coincident with a trough'' in the dust in the local interstellar medium found by Gaustad amp; Van Buren (1993). In addition, it is found that the Mathis-Rumpl-Nordsieck power-law size distribution must be modified to enhance the number of smaller particles for the regions with higher I_60\mum - I_100\mum flux density ratio.