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A&A Supplement Ser., Vol. 124, August, 385-395

Received July 29; accepted November 26, 1996

Studies of dense cores in regions of massive star formation

V. Structure and kinematics of dense cores from ammonia observationsgif

I. Zinchenkotex2html_wrap1571 - Th. Henningtex2html_wrap1573 - K. Schreyertex2html_wrap1575

Send offprint request: I. Zinchenko

tex2html_wrap1577  Institute of Applied Physics of the Russian Academy of Sciences, 46 Uljanov str., 603600 Nizhny Novgorod, Russia
tex2html_wrap1579  Helsinki University Observatory, Tähtitorninmäki, P.O. Box 14, FIN-00014 University of Helsinki, Finland
tex2html_wrap1581  Max Planck Society, Research Unit ``Dust in star-forming regions'', Schillergäßchen 3, D-07745 Jena, Germany


We present results of the observations of 17 molecular clouds associated with bright FIR sources in the tex2html_wrap_inline1545 (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_inline1547 are close to virial masses. However, in S 88 B the ratio tex2html_wrap_inline1549 is only tex2html_wrap_inline1551 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 most prominent example is S 255. S 87 has a two-component structure with 2 distinct velocity components which overlap partly spatially. In about half of the mapped sources the tex2html_wrap_inline1553 line widths increase near the peaks of the ammonia emission.

The kinetic temperatures are centrally peaked. They reach tex2html_wrap_inline1555 in the centre and drop to tex2html_wrap_inline1557 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_inline1559 relative to the core emission was detected. Hyperfine intensity anomalies in the (1, 1) transition were found in S 199 in addition to the known case of these anomalies in S 87.

keywords: stars: formation -- ISM: clouds -- ISM: molecules -- radio lines: interstellar

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