In the molecular cloud G33.92+0.11A, massive stars are forming sequentially in dense cores, probably due to interaction with accreted gas. Cold dense gas, which is likely the pristine gas of the cloud, is traced by DCN line and dust continuum emission. Clear chemical differences were observed in different source locations and for different velocity components in the same line of sight. Several distinct gas components coexist in the cloud: the pristine cold gas, the accreted dense gas, and warm turbulent gas, in addition to the star-forming dense clumps. Filaments of accreted gas occur in the northern part of the A1 and A5 clumps, and the velocity gradient along these features suggests that the gas is falling toward the cloud and may have triggered the most recent star formation. The large concentration of turbulent gas in the A2 clump seems to have formed mainly through disturbances from the outside.

Introduction
Data
    ALMA Observations
    Observed Molecules
Results and Discussion
    Different Velocity Components
    Velocity Gradients along the Filamentary Features
    Comparison of Emission Distributions
    Sequential Star Formation
Summary
Acknowledgments
References

• YOUNG CHOL MINH(Korea Astronomy and Space Science Institute, 776 Daedeok-daero, Yuseong, Daejeon 34055Korea)
• HAUYU BAOBAB LIU(Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617Taiwan)
• HUEI-RU VIVIEN CHEN(Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013Taiwan)