Dust emission and molecular depletion in L1498

We present 100 and 200 mu m ISOPHOT observations of the dense core L1498. We have mapped the central core by using Delta I-200 = I-200 - I-100/theta, where Delta I-200 is a measure of the emission from the cold dust and theta = I-100/I-200 in the outer regions. The dust continuum emission provides information about the chemical depletion and the properties of cold cores where there is a lack of gas tracers. Previous observations of L1498 show that the emission from CS and CCS lies outside of the NH3 core. The peak in Delta I-200 lies close to the previously observed NH3 peak. A comparison with high spatial resolution observations of (CO)-O-18 emission shows that the Delta I-200 maximum coincides with a dip in the (CO)-O-18 emission at the core center. We estimate that the depletion factor for (CO)-O-18 in this region is at least 8 and is likely to be much larger. Such high depletion has significant implications for studies of gas-grain chemistry and protostellar cores.