2017ApJ...844...68T

We carried out line survey observations at the 26-30 GHz band toward the four high-mass star-forming regions containing hot cores, G10.30-0.15, G12.89+0.49, G16.86-2.16, and G28.28-0.36, with the Robert C. Byrd Green Bank Telescope. We have detected HC₅N from all of the sources, and HC₇N from the three sources, except for G10.30-0.15. We further conducted observations of HC₅N at the 42-46 GHz and 82-103 GHz bands toward the three sources, G12.89+0.49, G16.86-2.16, and G28.28-0.36, with the Nobeyama 45 m radio telescope. The rotational lines of HC₅N with the high-excitation energies (E_u/k∼63–100 K), which are hardly excited in the cold dark clouds, have been detected from the three sources. The rotational temperatures of HC₅N are found to be ∼13-20 K in the three sources. The detection of the lines with the high-excitation energies and the derived rotational temperatures indicate that HC₅N exists in the warm gas within 0.07-0.1 pc radii around massive young stellar objects. The column densities of HC₅N in the three sources are derived to be (∼2.0-2.8) × 10¹³ cm^–2. We compare the ratios between N(HC₅N) the column density of HC₅N and W(CH₃OH) the integrated intensity of the thermal CH₃OH emission line among the three high-mass star-forming regions. We found a possibility of the chemical differentiation in the three high-mass star-forming regions; G28.28-0.36 shows the largest N(HC₅N)/W(CH₃OH) ratio of 8.0×10¹⁴ in units of (K km s^–1)^–1 cm^–2, while G12.89+0.49 and G16.86-2.16 show the smaller values (∼2×10¹³).