大质量恒星形成区中稠密核的射电干涉仪观测研究

发布时间：2018-04-12 13:37

  本文选题：星际介质 + 分子云　； 参考：《南京大学》2016年博士论文

【摘要】：大质量恒星,通常指8倍太阳质量以上的恒星,在天体物理各领域的研究中都有重要的影响。它们主导了星团的光度,其强烈的星风、紫外波段的发射、死亡时的超新星爆发剧烈地影响星际介质的构成和能量平衡,所以研究其如何形成具有重要的意义。对于大质量恒星形成,近十年的观测和理论研究取得了很多进展,例如我们已经明确,大质量恒星诞生于分子云中的大质量稠密核内,并且倾向于成团形成。然而,若干有关大质量稠密核的重要问题仍然没有得到解决。例如:大质量稠密核是否普遍处在位力平衡状态;湍动和磁场对稠密核的形成和演化有何作用;星系中心附近的极端物理环境下稠密核的形成是否受到影响。因此,本文根据对银河系内若干大质量恒星形成区的亚毫米波和射电波段的高空间分辨率观测,讨论了三个问题:1)大质量恒星形成区中稠密核的统计性质;2)处在早期演化阶段的大质量团块的碎裂过程和稠密核的动力学状态;3)银河系中心附近分子云中的大质量稠密核性质。这三个问题从不同角度探讨了大质量稠密核的形成和塌缩过程,对于理解大质量恒星的形成有重要意义。与上述三个问题对应,我们具体介绍了三项观测研究:·对62个大质量恒星形成区的甚大阵氨分子谱线巡测,以得到稠密核的温度、线宽、质量、位力参数等统计性质;·对红外暗云G28.53-0.25的(增容)甚大阵氨分子谱线和脉泽、绿堤射电望远镜氨分子谱线以及亚毫米波射电望远镜阵尘埃连续谱和分子谱线的综合观测,以研究团块的碎裂和稠密核的动力学状态以及恒星形成活动;·对中央分子带中6块巨分子云的央斯基甚大阵氨分子谱线、水脉泽和射电连续谱,以及亚毫米波射电望远镜阵连续谱和分子谱线的观测,以研究其中的稠密气体分布和恒星形成活动。我们发现,在约1 pc尺度的团块或纤维进一步碎裂过程中,只考虑热运动的支撑作用得到的碎裂产物质量一般只有几个M(?),远小于观测到的稠密核质量,而考虑湍动的支撑作用后,碎裂的结果与稠密核质量一致,使得大质量稠密核的形成成为可能。另一方面,中央分子带中缺乏内部致密结构的几个分子云似乎暗示极强的湍动也会阻止碎裂过程和后续稠密核的形成,导致恒星形成活动不活跃。这表明大质量稠密核的形成过程中湍动起到重要作用。另外我们发现,在只考虑湍动和热运动支撑作用的情况下,稠密核的位力参数普遍小于临界值,表明它们是自引力束缚的。其中较大质量的稠密核的位力参数普遍远小于1,表明它们严重偏离位力平衡状态。考虑到这些稠密核不可能是暂现式的结构,我们需要额外的支撑作用使其更接近位力平衡,一个可能的机制是磁场的支撑。这表明磁场和湍动在控制大质量稠密核的动力学状态中可能是同等重要的。
[Abstract]:Large-mass stars, usually those above 8 times the mass of the sun, play an important role in all fields of astrophysics.They dominate the luminosity of star clusters, their strong star winds, ultraviolet emission, and supernova bursts at the time of death have a dramatic impact on the composition and energy balance of interstellar media, so it is of great significance to study how to form them.For the formation of massive stars, much progress has been made in the observation and theoretical studies in the past decade. For example, we have made it clear that large mass stars are born in dense nuclei in the molecular cloud and tend to form clusters.However, some important problems concerning mass dense nuclei are still unsolved.For example, whether large mass dense nuclei are generally in the state of potential force equilibrium, what are the effects of turbulence and magnetic field on the formation and evolution of dense nuclei, and whether the formation of dense nuclei is affected in the extreme physical environment near the center of galaxies.Therefore, based on the high spatial resolution observations of submillimeter waves and radio bands in several massive star forming regions of the Milky way Milky way,In this paper, we discuss three problems: 1) Statistical properties of dense nuclei in the mass star formation region (2) fragmentation of mass masses in the early stage of evolution and 3) large mass dense nuclei in molecular clouds near the center of the Milky way Galaxy.These three problems discuss the formation and collapse process of dense nuclei with large mass from different angles, which is of great significance for understanding the formation of massive stars.Corresponding to the above three problems, we have introduced three observational studies in detail: the very large ammonia molecular spectral line survey in 62 large mass star forming regions is used to obtain the temperature, linewidth, mass of dense nuclei.Statistical properties such as potential force parameters, comprehensive observation of (capacitive) very large ammonia molecular spectra and maser lines of infrared dark clouds G28.53-0.25, ammonia molecular spectra lines of the Green Dike Radio Telescope and dust continuous spectrum and molecular spectral lines of the submillimeter wave radio telescope array,In order to study the dynamic state of fragmentation and dense nuclei and the activity of star formation in the lumps, the Yansky very large array of ammonia molecular lines, water maser and radio continuous spectra of 6 giant molecular clouds in the central molecular band are studied.The continuous spectra and molecular spectral lines of the submillimeter wave radio telescope array are also observed to study the dense gas distribution and star formation activities.It is found that in the further fragmentation of a mass or fiber on the scale of about 1 PC, the mass of the broken product obtained by considering only the support of thermal motion is generally only a few Mucks, which is much smaller than the observed mass of dense nuclei.Considering the support of turbulence, the result of fragmentation is consistent with the mass of dense nucleus, which makes the formation of large mass and dense nucleus possible.On the other hand, several molecular clouds lacking internal dense structures in the central molecular band seem to imply that extremely strong turbulence may also prevent the fragmentation process and the subsequent formation of dense nuclei, resulting in the inactivity of star formation.This indicates that turbulence plays an important role in the formation of large mass dense nuclei.In addition, we find that the potential force parameters of dense nuclei are generally smaller than the critical values, which indicates that they are bound by self-gravity.The potential force parameters of the dense nuclei with larger mass are generally much less than 1, indicating that they deviate seriously from the potential force equilibrium state.Considering that these dense nuclei cannot be temporary structures, we need additional support to make them closer to the potential force balance. One possible mechanism is magnetic field support.This suggests that the magnetic field and turbulence may be equally important in controlling the dynamic state of dense nuclei with large mass.
【学位授予单位】：南京大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P152;P161
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本文编号：1739975