Astronomy and Astrophysics, volume 314, 265-274 (1996/10-1)
15NH3 towards ultracompact HII regions.
WYROWSKI F. and WALMSLEY C.M.
Abstract (from CDS):
We have observed the (3,3) and (4,4) lines of 15NH3 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, 14NH3(3,3) was observed in 6 sources and the (4,2) and (5,4) non-metastable transitions of 14NH3 were detected in G10.47+0.03 and G31.41+0.31. We find beam averaged 15NH3 column densities of order 1013cm–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 15NH3(3,3) transition like those found in NGC 7538 by Mauersberger et al. (1986). The non-detection of 15NH3(4,3) in G10.47+0.03 and G31.41+0.31 allows us to set an upper limit of 5x107cm–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 14NH3 we find column densities lower by a factor of 3-4 using 15NH3. Possible explanations of this discrepancy are discussed.
ISM: clouds - ISM: molecules - radio lines: ISM