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5. Summary and conclusions

  We have presented results of the observations of 17 molecular clouds associated with bright FIR sources in the tex2html_wrap_inline2351 (1, 1) and (2, 2) lines with the 100-m radio telescope in Effelsberg. The lines were detected in 11 clouds and 10 of them have been mapped in these lines. The kinetic temperatures, sizes, masses and mean densities of the ammonia cores have been derived.

For most of the detected clouds the masses derived under the assumption of a relative ammonia abundance of tex2html_wrap_inline2353 are close to virial masses. However, in S 88 B the ratio tex2html_wrap_inline2355 is only tex2html_wrap_inline2357 and in a few other cases this ratio is significantly lower than unity which may indicate ammonia underabundance. Almost all objects with the signs of underabundance are among the most luminous IR sources in our sample.

Most of the mapped cores are elongated with noticeable velocity gradients along the major axis. The highest elongation and velocity gradient are observed in S 255. S 87 has a two-component structure with 2 distinct velocity components which overlap partly spatially. In about a half of the mapped sources the tex2html_wrap_inline2359 line widths increase near the peaks of the ammonia emission.

The kinetic temperatures are centrally peaked. They reach tex2html_wrap_inline2361 in the center and drop to tex2html_wrap_inline2363 at the edges of the ammonia emitting regions.

In S 76 E a weak extended emission in the (1, 1) line at the velocity blue-shifted by tex2html_wrap_inline2365 relative to the core emission was detected. Hyperfine intensity anomalies in the (1, 1) transition are noticeable in S 199 in addition to S 87 which is a known case of these anomalies.

Acknowledgements

We thank J. Harju and C. Henkel for the helpful discussions, W.J. Altenhoff for providing calibration data for the 100-m antenna, K. Mattila for critical reading the manuscript and the anonymous referee for valuable suggestions which improved the presentation of the results. Special thanks are to C.M. Walmsley for many fruitful discussions and invaluable assistance at various stages of this work. I.Z. is very grateful to the MPG-AG ``Staub in Sternentstehungsgebieten'' for the hospitality. He was also supported in part by the INTAS grant 93-2168 and grant 94-02-04861-a from the Russian Foundation for Basic Research.


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