大质量恒星形成:外向流和绿色延展天体
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摘要
恒星作为宇宙的基础组成元素,其形成过程一直是天文学中的重要研究对象。人们已基本了解中小质量恒星(质量小于8M_⊙)的形成和演化过程;受到数量少、嵌埋深、演化快和反馈剧烈等因素的影响,大质量恒星(质量大于8M_⊙)的形成过程依然谜团重重。介绍了小质量恒星形成的基本理论,以及吸积盘、竞争吸积、并合三种主流的大质量恒星形成模型;回顾了以往使用红外或射电望远镜对大质量恒星形成区的观测和分析,以及现阶段使用多波段巡天观测手段对大质量恒星形成区的研究成果;着重介绍了目前公认的大质量恒星形成的示踪物——分子外向流的理论和观测现状,以及大质量外向流的优秀候选体——绿色延展天体的发现、理论及观测研究情况。最后,对大质量恒星形成的理论和观测研究进行了总结和展望。
As the main contributor of radiation and chemical enrichment of the universe,stars are the key targets for astronomical investigations. Therefore, it is crucial to figure out how stars and especially massive stars form in molecular clouds. The scenario of lowmass star formation has been well established. However the formation of high-mass stars(>8 M⊙) has been elusive for decades as high-mass star-forming regions are rare, always deeply embedded, the timescales are considerably short, and the natal environs are inevitably destroyed by strong feedbacks. We present here, the fundamental theoretical models and observational facts of star formation, which are followed by a summary of recent findings based on observations in infrared and radio bands. Additionally, molecular outflows which can serve as an excellent tracer of early phases of high-mass star formation(HMSF) are introduced. Up-to-date investigations of extended green objects, which are candidates of massive outflows, have provided new constraints on the HMSF models. The by-far status of HMSF studies is summarized and future perspectives are given in the last part of this paper.
As the main contributor of radiation and chemical enrichment of the universe,stars are the key targets for astronomical investigations. Therefore, it is crucial to figure out how stars and especially massive stars form in molecular clouds. The scenario of lowmass star formation has been well established. However the formation of high-mass stars(>8 M⊙) has been elusive for decades as high-mass star-forming regions are rare, always deeply embedded, the timescales are considerably short, and the natal environs are inevitably destroyed by strong feedbacks. We present here, the fundamental theoretical models and observational facts of star formation, which are followed by a summary of recent findings based on observations in infrared and radio bands. Additionally, molecular outflows which can serve as an excellent tracer of early phases of high-mass star formation(HMSF) are introduced. Up-to-date investigations of extended green objects, which are candidates of massive outflows, have provided new constraints on the HMSF models. The by-far status of HMSF studies is summarized and future perspectives are given in the last part of this paper.
引文
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[2] Barret A. IEEE Transactions on Antennas and Propagtion, 1964, 12:822
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[16] Churchwell E. A&ARv, 1990, 2:79
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