Chemical Diversity in Three Massive Young Stellar Objects Associated with 6.7 GHz CH3OH Masers

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).