射电天文研究室知识库

The excitation of H2O masers usually needs very high density gas, hence it can serve as a marker of dense gas in HII region. We selected a sample of H2O maser sources from Plume et al. (four with, and four without detected CS(J = 7 - 6) emission), and observed them ill (CO)-C-13(j = 1-0) and (CO)-O-18 (j = 1-0). (CO)-O-18 (J = 1-0) emission was detected only in three of the sources with detected CS(J = 7-6) emission. An analysis combined with some data in the literature suggests that these dense cores may be located at different evolutionary stages. Multi-line observation study may provide us clues on the evolution of massive star forming regions and the massive stars themselves.