Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996a%26a...314..265w&link_type=abstract
Astronomy and Astrophysics, v.314, p.265-274
Astronomy and Astrophysics
Astrophysics
10
Ism: Clouds, Ism: Molecules, Radio Lines: Ism
Scientific paper
We have observed the (3,3) and (4,4) lines of ^15^NH_3_ toward a selection of ultracompact Hii regions using the Effelsberg 100m telescope. The lines were detected in 6 sources. Toward the strong source G10.47+0.03, all metastable inversion transitions from (1,1) to (6,6) were detected. In addition, ^14^NH_3_(3,3) was observed in 6 sources and the (4,2) and (5,4) non-metastable transitions of ^14^NH_3_ were detected in G10.47+0.03 and G31.41+0.31. We find beam averaged ^15^NH_3_ column densities of order 10^13^cm^-2^ and temperatures between 100 and 300K. Towards G10.47+0.03, the rotational temperature between metastable levels is found to be 185+/-20K. Comparison with an LVG model allows us to deduce a kinetic temperature of 240+/-40K. No evidence is found for maser characteristics in the ^15^NH_3_(3,3) transition like those found in NGC 7538 by Mauersberger et al. (1986). The non-detection of ^15^NH_3_(4,3) in G10.47+0.03 and G31.41+0.31 allows us to set an upper limit of 5x10^7^cm^-3^ to the molecular hydrogen density in the hot cores. In comparison to column densities based upon optical depths derived from the relative intensities of hyperfine satellites of ^14^NH_3_ we find column densities lower by a factor of 3-4 using ^15^NH_3_. Possible explanations of this discrepancy are discussed.
Walmsley Charles Malcolm
Wyrowski Frank
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