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A Survey and Statistics of Interstellar OH and H_2O masers

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Chinese Journal of Astronomy and Astrophysics 2005年第2期5卷 175-183页

作者： Han-PingLiu J.R.Forster JinSun DepartmentofPhysics BeijingNormalUniversityBeijing100875 UniversityofCalifornia BerkeleyandHatCreekRadioObservatory42231BidwellRoadHatCreekCA96040 DepartmentofAstronomy BeijingNormalUniversityBeijing100875

We present a statistical analysis of a sky survey of interstellar H2O and OH masers. These masers can be classified into three categories: isolated H2O masers, isolated OH masers, and simple OH/H2O maser associations. The total number of sources in each category is of the same order of magnitude, and as an evolutionary phase they can maintain ~ 105 yr. An improved radiative pumping mechanism is proposed. This model avoids some of the deficiencies of previous radiative models, such as shortage of exciting photons. The statistical results obtained from the survey can be interpreted by the new mechanism together with the evolutionary model in which the gravitational force of the central stellar objects is responsible for the HII region.

关键词： surveys masers radiation mechanism: non-thermal HII regions

The potential of FAST in detecting celestial hydroxyl masers and related science topics

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Research in Astronomy and Astrophysics 2019年第2期19卷 65-70页

作者： Jiang-Shui Zhang Di Li Jun-Zhi Wang Qing-Feng Zhu Juan Li Center for Astrophysics Guangzhou University National Astronomical Observatories Chinese Academy of Sciences Key Laboratory of FAST National Astronomical Observatories Chinese Academy of Sciences School of Astronomy and Space Science University of Chinese Academy of Sciences Shanghai Astronomical Observatory Chinese Academy of Sciences University of Science and Technology of China Chinese Academy of Science

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) will make contributions to studies of Galactic and extragalactic masers. This telescope, with construction finished and now undergoing commissioning, has an innovative design that leads to the highest sensitivity of any single dish radio telescope in the world. FAST's potential for OH megamaser research is discussed, including the sky density of masers detectable in surveys. The scientific impact expected from FAST maser studies is also discussed.

关键词： masers instrumentation:sensitivity instrumentation:detectability sky density galaxies:interactions

First MERLIN Observations of Line Emission from the OH Megamaser toward IRAS 10173+0828

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Chinese Journal of Astronomy and Astrophysics 2005年第2期5卷 159-164页

作者： Zhi-YaoYu ShanghaiAstronomicalObservatory ChineseAcademyofSciencesShanghai200030

Many galaxies are thought to contain massive black holes, with masses in excess of ten million solar masses, at their centres and warped circumnuclear toruses. The best evidence comes from observing gas or masers rotating rapidly within a circumnuclear torus surrounding a central body. Here we report on the first MERLIN observations of line emission from the OH megamaser toward IRAS 10173+0828. The position of peak flux contours of the OH megamaser is consistent with that of the continuum in IRAS 10173+0828. This means that the OH megamaser is a diffuse unsaturated maser which could amplify the diffuse 18 cm continuum emission with an amplification factor of order unity.

关键词： masers ISM: molecules galaxies: nuclei galaxies: active galaxies:kinematics and dynamic galaxies: ISM

The spiral structure of the Milky Way

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Research in Astronomy and Astrophysics 2018年第12期18卷 9-28页

作者： Ye Xu Li-Gang Hou Yuan-Wei Wu Purple Mountain Observatory Chinese Academy of Sciences CAS Key Laboratory of FAST National Astronomical Observatories Chinese Academy of Sciences National Astronomical Observatories Chinese Academy of Sciences National Time Service Center Key Laboratory of Precise Positioning and Timing Technology Chinese Academy of Sciences

The morphology and kinematics of the spiral structure of the Milky Way are long-standing problems in *** this review we firstly summarize various methods with different tracers used to solve this *** astrometry of Galactic sources is gradually alleviating this difficult situation caused mainly by large distance uncertainties, as we can currently obtain accurate parallaxes(a few μas) and proper motions(≈1 km s-1) by using Very Long Baseline Interferometry(VLBI).On the other hand, the Gaia mission is providing the largest, uniform sample of parallaxes for O-type stars in the entire Milky *** upon the VLBI maser and Gaia O-star parallax measurements, nearby spiral structures of the Perseus, Local, Sagittarius and Scutum Arms are determined in unprecedented ***, we estimate fundamental Galactic parameters of the distance to the Galactic center,R0, to be 8.35 ± 0.18 kpc, and circular rotation speed at the Sun, Θ0, to be 240±10 km *** found kinematic differences between O stars and interstellar masers: the O stars, on average, rotate faster,>8 km s-1than maser-traced high-mass star forming regions.

关键词： Galaxy:structure Galaxy:kinematics and dynamics masers techniques:high angular resolution astrometry stars:formation

Statistical Properties of 6.7 GHz Methanol Maser Sources

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Chinese Journal of Astronomy and Astrophysics 2003年第1期3卷 49-68页

作者： YeXu Xing-WuZheng Dong-RongJiang NationalAstronomicalObservatories ChineseAcademyofSciencesUrumqi830011／／ShanghaiAstronomicalObservatoryChineseAcademyofSciencesShanghai200030 DepartmentofAstronomy NanjingUniversityNanjing210093 ShanghaiAstronomicalObservatory ChineseAcademyofSciencesShanghai200030

We present a statistical analysis of 482 6.7 GHz methanol maser sources from the available literature, on their maser emission and the characteristics of their associated infrared sources. On the color-color diagram, more than 70% of the objects fall within a very small region (0.57 ≤ [25-12] ≤ 1.30 and 1.30 ≤ [60-12] ≤ 2.50). This suggests that 6.7 GHz methanol maser emission occurs only within a very short evolutionary phase during the earliest stage of star formation. The velocity ranges of the masers belong to two main groups: one from 1 to 10 km s?1, and one from about 11 to 20 km s?1. These velocity ranges indicate that the masers are probably associated with both disks and outflows. The correlations between the maser and infrared flux densities, and between the maser and infrared luminosities, suggest that far-infrared radiation is a possible pumping mechanism for the masers which most probably originate from some outer molecular envelopes or disks.

关键词： masers ISM: molecules stars: circumstellar matter stars: formation ISM: HII regions

An H_2O flare in GGD25

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Chinese Science Bulletin 2001年第1期46卷 35-39页

作者： XU Ye, ZHENG Xingwu JIANG Dongrong, ZHANG Fujun& YU Zhiyao1. Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China 2. Chinese National Observatories, Chinese Academy of Sciences, Beijing 100080, China 3. Department of Astronomy, Nanjing University, Nanjing 210093, China Shanghai Astronomical Observatory Chinese Academy of Sciences Shanghai China Chinese National Observatories Chinese Academy of Sciences Beijing China Department of Astronomy Nanjing University 210093 China

We report the observing results of a short time scale monitoring of the 22 GHz water maser emission in GGD25. A rapid water maser outburst with the time scales of 4 d has been detected, and the variations are accompanied by some changes in the line width. The time variations were probably caused by a collision pump which led to changes in the pump input.

关键词： interstellar masers (ISM) individual GGD25 masers.

Observations of Hydroxyl Maser Sources at 18-cm Band

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Chinese Science Bulletin 1994年第15期39卷 1281-1284页

作者：张坚罗先汉王建华季德盛 Geophysics Department Peking University Beijing 100871 PRC Shanghai Observatory Shanghai 200030 PRC

1 Introduction Since the first OH maser source was detected in 1965, the astronomical masers have been used as powerful probes for the study of the early activities of stars and evolutions of stats. Among all the presently known maser sources, as it has a wide distribution and intense emission, and intimately associates with the early and late stages of stellar evolution, the OH maser has drawn a lot of attention and

关键词： spectrometer OH masers evolution of star.

An Environmental Perception System to Autonomous OffRoad Navigation by using Multi-sensor Data Fusion

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An Environmental Perception System to Autonomous OffRoad Nav...

Disk-Outflow Models as Applied to High Mass Star Forming Regions through Methanol and Water Maser Observations

2005 International Conference on Neural Networks and Brain(ICNN&B’05)

作者： Zhiyu Xiang Dept.of Information and Electronic Engineering Zhejiang University

ISBN: (纸本)0780394224;9780780394223

＜正＞Environmental perception is one of the most difficult problems on the research of off-road autonomous *** paper describes a multisensor data fusion based environmental’ perception system for off-road autonomous *** system is composed of one camera,four laser range finders, one microwave radar,and several ultrasonic sensors.A hierarchical structure is used to organize the sensors from feature level to high fusion level.A 2D fusion map consisting six classifications is proposed to describe the surrounding ***-Shafer evidence theory is adopted to decide the classification of each grid in the fusion map.A weighted evidence combination rule is proposed and implemented to improve the decision results under high conflicting *** experimental results show that the proposed system is reliable and is able to fulfill the requirements from off-road navigation.

关键词： Navigation Laser radar Remotely operated vehicles Mobile robots Cameras Laser fusion Laser theory masers Sensor systems Microwave sensors

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International Journal of Astronomy and Astrophysics 2014年第4期4卷 571-597页

作者： Hontas F. Farmer Department of Physical Science Richard J. Daley College City Colleges of Chicago Chicago IL USA

As the recent publication by Breen et al. (2013) found, Class II methanol masers are exclusively associated with high mass star forming regions. Based on the positions of the Class I and II methanol and H2O masers, UC H II regions and 4.5 μm infrared sources, and the center velocities (vLSR) of the Class I methanol and H2O masers, compared to the vLSR of the Class II methanol masers, we propose three disk-outflow models that may be traced by methanol masers. In all three models, we have located the Class II methanol maser near the protostar, and the Class I methanol maser in the outflow, as is known from observations during the last twenty years. In our first model, the H2O masers trace the linear extent of the outflow. In our second model, the H2O masers are located in a circumstellar disk. In our third model, the H2O masers are located in one or more outflows near the terminating shock where the outflow impacts the ambient interstellar medium. Together, these models reiterate the utility of coordinated high angular resolution observations of high mass star forming regions in maser lines and associated star formation tracers.

关键词： masers Methanol Massive Star Formation Stars: Evolution Stars: Distances