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

Abstract

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 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 ( 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) 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 in units of (K km s−1)−1 cm−2, while G12.89+0.49 and G16.86–2.16 show the smaller values ( ).