Abstract
Abstract We have carried out observations in the 42–46 and 82–103 GHz bands with the Nobeyama 45 m radio telescope, and in the 338.2–339.2 and 348.45–349.45 GHz bands with the ASTE 10 m telescope, toward three high-mass star-forming regions containing massive young stellar objects (MYSOs), G12.89+0.49, G16.86−2.16, and G28.28−0.36. We have detected HC3N including its 13C and D isotopologues, CH3OH, CH3CCH, and several complex organic molecules. Using our previous results for HC5N in these sources, we compare their N(HC5N)/N(CH3OH) ratios. The ratio in G28.28−0.36 is derived to be , which is higher than that in G12.89+0.49 by one order of magnitude, and higher than in G16.86−2.16 by a factor of ∼5. We investigate the relationship between the N(HC5N)/N(CH3OH) and the N(CH3CCH)/N(CH3OH) ratios. The relationships of the two column density ratios in G28.28−0.36 and G16.86−2.16 are similar to each other, while HC5N is less abundant compared to CH3CCH in G12.89+0.49. These results imply a chemical diversity in the lukewarm (T ∼ 20–30 K) envelope around MYSOs. In addition, several spectral lines from complex organic molecules, including very-high-excitation energy lines, have been detected toward G12.89+0.49, while the line density is significantly low in G28.28−0.36. These results suggest that organic-poor MYSOs are surrounded by a carbon-chain-rich lukewarm envelope (G28.28−0.36), while organic-rich MYSOs, namely hot cores, are surrounded by a CH3OH-rich lukewarm envelope (G12.89+0.49 and G16.86−2.16).
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