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

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 {0.091}_-0.039^+0.109, 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).