SIMBAD references

We surveyed 81 dense molecular cores associated with regions of massive star formation and Sgr A in the J_K-1_K1=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 E_u/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 10_0,10-9_0,9 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.