Session 117 - Galactic ISM.
Oral session, Thursday, January 16
Harbour B,

## [117.04] Infrared Identification of Cold Molecular Regions

S. J. Carey, F. O. Clark (Phillips Lab/GPOB)

We describe a new method following the prescription of Laureijs et al. (1991) for identifying cold molecular cores using the 60 and 100 \mu m observations from the IRAS satellite. \Delta I_100 = I_100 - I_60 / \theta, where \theta is the average 60/100 ratio (\sim 0.2) for the diffuse ISM, is shown to be a sensitive diagnostic of cold (non star forming) regions with densities in excess of 10^3 \: cm^-3. Through investigation of the IRAS Sky Survey Atlas for fields containing Lynds 1457, the Pleiades molecular cloud, the Polaris flare clouds and MBM 53-55, we determine that \Delta I_100 > 2.0 \: MJy/sr is an accurate tracer of cold molecular material. In addition, our method efficiently traces material in the presence of a radiation field greater than the interstellar radiation field (HII regions, sites of embedded star formation) as regions of \Delta I_100 < -2.0 \: MJy/sr. We present a \Delta I_100 image revealing substantial cold dense material to the south of MBM 53 as conjectured by Magnani, Blitz and Mundy (1985).

This work was performed while S.\ J.\ C.\ held a National Research Council-Phillips Laboratory Research Associateship.