Observations of Cyanopolyynes toward Four High-mass Star-forming Regions Containing Hot Cores

Abstract

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 HC 5 N from all of the sources, and HC 7 N from the three sources, except for G10.30–0.15. We further conducted observations of HC 5 N 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 HC 5 N with the high-excitation energies ( K), which are hardly excited in the cold dark clouds, have been detected from the three sources. The rotational temperatures of HC 5 N 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 HC 5 N exists in the warm gas within 0.07–0.1 pc radii around massive young stellar objects. The column densities of HC 5 N in the three sources are derived to be (∼2.0–2.8) cm −2 . We compare the ratios between N (HC 5 N) the column density of HC 5 N and W (CH 3 OH) the integrated intensity of the thermal CH 3 OH 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 (HC 5 N)/ W (CH 3 OH) ratio of in units of (K km s −1 ) −1 cm −2 , while G12.89+0.49 and G16.86–2.16 show the smaller values ( ).