Preprotostellar core properties from far-infrared observations

We, present the results of far-infrared ISOPHOT observations of the preprot ostellar cores L1498, B133, and B68. Comparison of the 100 and 200 mum data suggest the presence of two dust temperatures along the line, of sight. Us ing a two-temperature model that assumes a cold central core surrounded by a slightly warmer envelope, we have isolated the 200 mum emission from the cold core. We use 160 and 1300 mum observations where available together wi th the isolated 200 mum data to derive a dust temperature for the core. The radial mass and density distributions were determined in each core, and th e stability of the cores was considered by comparing the mass estimates fro m the 200 Pm data with the virial masses. The cores can be divided into thr ee regions with different radial density dependences, each of which can be described by a power law rho proportional to r(-alpha) : a relatively flat inner region with alpha similar to 1.2, a steeper region with alpha similar to 1.8, and a very sharp outer edge with alpha greater than or similar to 4. These power-law results are in agreement with other derivations of prepr otostellar core density profiles. The results presented here are also consi stent with several different models of core evolution. In addition, we find that the inner regions of the core are less bound than the outer ones, sug gesting that the outer layers are confining the central regions.