Astronomy and Astrophysics, volume 361, 1079-1094 (2000/9-3)
HNCO in massive galactic dense cores.
ZINCHENKO I., HENKEL C. and MAO R.Q.
Abstract (from CDS):
We surveyed 81 dense molecular cores associated with regions of massive star formation and Sgr A in the JK-1K1=505-404 and 10010-909 lines of HNCO. Line emission was detected towards 57 objects. Selected subsamples were also observed in the 101-000, 404-303, 707-606, 15015-14014, 16016-15015 and 21021-20020 lines, covering a frequency range from 22 to 461GHz. HNCO lines from the K–1 = 2,3 ladders were detected in several sources. Towards Orion-KL, K–1 = 5 transitions with upper state energies Eu/k∼1100 and 1300K could be observed. Five HNCO cores were mapped. The sources remain spatially unresolved at 220 and 461GHz (10010-909 and 21010-20020 transitions) with beam sizes of 24" and 18", respectively. The detection of hyperfine structure in the 101-000 transition is consistent with optically thin emission under conditions of Local Thermodynamic Equilibrium (LTE). This is corroborated by a rotational diagram analysis of Orion-KL that indicates optically thin line emission also for transitions between higher excited states. At the same time a tentative detection of interstellar HN13CO (the 100,10-90,9 line at 220GHz toward G 310.12-0.20) suggests optically thick emission from some rotational transitions. Typical HNCO abundances relative to H2 as derived from a population diagram analysis are ∼10–9. The rotational temperatures reach ∼500 K. The gas densities in regions of HNCO K–1=0 emission should be n>106cm–3 and in regions of K–1>0 emission about an order of magnitude higher even for radiative excitation. HNCO abundances are found to be enhanced in high-velocity gas. HNCO integrated line intensities correlate well with those of thermal SiO emission. This indicates a spatial coexistence of the two species and may hint at a common production mechanism, presumably based on shock chemistry.
stars: formation - ISM: clouds - ISM: molecules - radio lines: ISM
VizieR on-line data:
<Available at CDS (J/A+A/361/1079): tables 1, 2, 5 to 14>
Erratum vol. 363, p. 1195 (2000)
Tables 1, 2: col(1): masers in SIMBAD, [ZMT95] or [ZPT98] or [HLB98] or [PCC93], col(Remarks): source containing the maser. In abstract : G 310.12-0.20 misprint for 301.12 (in SIMBAD : [BE83] Maser 301.12-00.20)
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