Molecular Spectra In Massive Star Forming Regions

We have analyised the observed results of low and high spatial resolution observations of molecular line emission toward regions of high-mass star formation which have contributed to the understanding of the physical conditions, morphologies, and dynamics of the molecular gas in the immediate vicinity of recently formed massive stars.Molecular outflows mark an important phase in the early evolution of star formation. Disks and outflows are ubiquitous during the birth of low-mass stars Although the two phenomena exist at very different spatial scales, but they are intimately connected. There are two different ideas about the massive star formation. Some investigators suggest that high-mass stars form via dynamical collapse of cloud cores, resulting in disk accretion and molecular outflows, similar to their low-mass counterparts; Some peoples suggest that high-mass stars form by the coalescence of low- to intermediate-mass stars. Because of the connection between outflow and accretion seen in low-mass stars, surveys of molecular outflows in high-mass YSOs can shed light on this debate. To search for high-velocity molecular emission toward massive star formation regions, and To study the connections between H2O masers, IRAS objects and outflow properties, we carried out a CO observation for a H2O maser sample. We found that most of the objects have excess high velocity emission produced by outflows; We find a significant correlation between CO line full widths and IRAS luminosities. The widths are proportional to the IRAS luminosities. It suggests that high velocity outflow is easier to occur in massive star formation region.Besides acting as powerful signposts of active star formation, the intense maser emission provides a unique tool to probe the physical conditions and kinematics of these regions on scales of 10 - 103 AU. In order to better understand the excited mechanism of masers, we have studied the time variability of 22 GHz H2O masers in GGD25, An outburst with the time scales of 4 day was detected. The time variation was probably caused by a collsion pump which led to changes in the pump input. This indicates that there are a lot of high density clumps with different velocities around the massive star formation, which is likely to originate from outflow. To understand the connections between methanol masers and other phenomena typical of star formation region, such as the associated far-infrared sources, we have investigated statistical properties of all known 6,7 GHz methanol maser sources. The result suggests that 6,7 GHz methanol maser emission may appear only during a limited period of massive star formation. They may originate from disks or outflows and may beTo submit to Graduate School, Acadcmia Sinicapumped by far-infrared radiation.Hot ammonia molecular cores in the latest stage of evolution are intimately associated with. UC H II regions and are undergoing outflowing motions, which might be produced either by the expansion of the recently formed H II region or by the presence of molecular outflows. The VAL data of the IRS1 region in NGC7538 are reprocessed and investigated as a sample,...