KMS of Xinjiang Astronomical Observatory, CAS
| 猎户座分子云丝条结构太尺度观测研究和大质量恒星形成区IRAS18360-0537的高分辨率观测研究 | |
| Alternative Title | Extended Observations toward Filamentary Structures in Orion Molecular Cloud and High-Resolution Studies in High-Mass Star Formation Region IRAS 18360-0537 |
吴刚
| |
| Subtype | 博士 |
| Thesis Advisor | 加尔肯·叶生别克 |
| 2018-05 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Name | 理学博士 |
| Degree Discipline | 天体物理 |
| Keyword | 大质量恒星形成 巨分子云 丝条结构 大质量原恒星 |
| Abstract | 通过HI区、UV辐射、星风、超新星等作用，大质量恒星（~8M_sun）在星际介质和星系演化中都起到非常重要的作用。因此大质量恒星是如何形成是天体物理的一个非常重要的课题，同时也是星系物理研究的基础。但是由于非常遥远的距离、非常深埋和非常短的演化时标等原因，使得大质量恒星形区的观测非常具有挑战。在这种条件下，大质量恒星形成的理论存在较多争议。目前讨论较多的大质量恒星形成的理论包括单核吸积和竞争吸积两种模型。 近期的一些研究表明，大质量恒星形成的演化过程更多的和大质量分子云和星团的形成联系在一起。认为大质量恒星形成不再是一个静态的过程而是一个大尺度到小尺度持续供给的高度动态的过程。因此就需要我们从~10pc尺度的分子云到~0.01pc尺度的大质量云核同时开展研究。 在~10pc尺度，我们首先希望理解分子云的丝条结构在大质量恒星形成中起到什么作用。我们对猎户座北端的integral-shaped filamentISF）丝条结构做了氨分子成图观测。此观测使用了中国科学院新疆天文台南山射电望远镜。整个丝条结构，1.2°×0.6°，全采样覆盖。我们研究了ISF的形态、碎裂、运动学和温度等重要信息。从成图观测中，我们证认了6个“clump”和11个“sub-clump”结构。我们发现这些“clump”和“sub-clump”不是随机分布的，而是在ISF上等间距分布。各自的间隔为11.30±1.31（1.36±0.16pc）和7.18±1.19（0.86±0.14pc）。假设ISF的倾角为60度，这种等间距分布严格符合等温 sausage instability和湍动sausage instability预言的间隔（0.86pc和1.43pc）。此外我们发现了沿着ISF的速度梯度，我们通过多谱线拟合得到了旋转速度约为0.6kms-lpc-1。并以此推出，ISF的转动能是引力能的很小一部分。进一步通过分析线心速度图，我们发现OMC-1~5都位于振荡的极值位置，暗示着存在流向各个团块的吸积流。之后，我们得到了ISF的温度分布图并通过温度分布发现ISF的各个团块可能还处在非常早期的演化阶段。最后，结合上面的结果，我们给出了一个滞动柱状碎裂-热柱状碎裂-金斯碎裂的碎裂演化路径以及对于速度梯度的理解。之后，我们用了GBT对ISF区域的氨分子档案数据研究了氨分子的HIA（Hyperfine Intensity Anomaly）现象。HIA在分子云中普遍存在，但是我们对其产生机制并不清楚。之前的研究大多针对孤立的恒星形成区做统计研究，这样不利于在统一的物理化学环境下分析HIA的产生机制。因此我们希望可以通过整片分子云的成图研究在相似物理环境下得到HIA和哪些参量更具有相关性，进一步希望最终在物理上得以解释HHA现象。我们首先开发了HHA的海量数据的自动处理程序，并验证了其有很好的处理精度。通过ISF区域的GBT氨分子观测数据的初步研究发现，内卫星线和外卫星线有相反的HA值。我们也希望把我们的计算程序运用到正在开展的氨分子巡天数据中，希望可以在银河系尺度上了解HIA现象。 大质量恒星形成是否像小质量恒星一样由外流和吸积盘系统形成是研究大质量恒星形成的具体过程的热点问题。从上世纪90年代开始，大量的大质量恒星区的外流搜寻工作逐渐展开。之后的单天线和干涉仪的观测都表明外流在大质量恒星形成区中普遍存在。 如果假设外流和吸积盘是严格的成协，我们可以想象在大质量恒星形成区中也应该探测到很多的吸积盘结构。但是吸积盘在大质量恒星系形成区中探测率极低，而且大部分的吸积盘候选体都在10~10L。范围内。吸积盘的“缺失”，特别是在L>105L。范围内，是观测的选择效应（短时标/深埋/遥远的距离）还是来自于内禀的解释，比如湍动和竞争吸积模型，依然是一个待解决的问题。此外，我们还不能给出一个大质量恒星星周盘的清晰的物理图像。例如关于大质量恒星形成区的吸积盘本身的物理性质，如吸积盘质量、内外半径、厚度、旋转速度等参量，我们都不清楚。进一步吸积盘对于大质量恒星形成的吸积率和中心星的物理性质等的估算能够给出给为直接和准确的结果。因此我们又把视线放在微观，希望能在~0.01pc尺度上了解大质量恒星形成的具体过程。 在0.01pc尺度以下，我们对一个1.2×10L。的大质量恒星形成区IRAS18360-0537开展了VLA、SMA和VLBA的系统观测研究工作。该源的运动学距离为6.3kpc并可能是L>10L。范围内最好的吸积盘候选体。该源在SMA的1.3mm连续谱中分辨为MM1和MM2两个致密云核。其中MM1存在一个东北-西南方向的双极外流。并且在垂直的方向（西北-东南）存在一个旋转结构。此外，SMA的CN分子呈现典型的反P-Cygni轮廓，因此该源存在内落。MM1的VLA3.6cm、1.3cm和7mm 连续谱流量分别为0.42mJy、1.89mJy和4.86mly。结合SMA和VLA的数据，我们建立的能谱分布图（SED）显示该源仍处于非常早期的演化阶段。利用BeSSeL项目的档案数据，我们发现VLBA的水脉泽和外流成协，并且数据显示外流可能存在进动。 |
| Other Abstract | High-mass stars (-8M_sun) play a key role in the evolution of galaxies with their feedback and their synthesis and dispersal of heavy elements. Therefore a full understanding of the formation processes of high-mass stars is essential in its own right as wel as for realistic simulations of galaxy evolution. However, large distances, deeply embedded sites, and short Kelvin-Helmholtz time scales make observations of their formation processes challenging. Two main classes of massive star fomation theory are under active study, Core Accretion and Competitive Accretion Furthemore, recent studies reveal that the most likely evolutionary scenario for high-mass star formation, which emphasizes the link of high-mass star formation to massive cloud and cluster formation. This process, which is no longer quasi-static but simultaneously evolves with both cloud and cluster formation, need us to study the molecular cloud at～10pc to massive dense core at ～0.01pc simultaneously. Firstly at～10pc scale, we seektounderstand the roles filamentary structures playin high-mass star formation. We mapped the integral-shaped filament ISF) located at the northern end of the Orion A molecular cloud in NHs (1,1) and(2,2). The observations were made using the 25 meter radio telescope operated by the Xinjiang Astronomical Observatory, Chinese Academy of Sciences. The whole filamentary structure, about 1.2°×0.6, is uniformly and fully-sampled. We investigate the morphology, fragmentation, kinematics, and temperature properties in this region. We identify 6' clumps' related to the well known OMC-1 to OMC-5 and 11' sub-clumps' within the map. The clumps and sub-clumps are separated not randomly but in roughly equal intervals along the ISF. The average spacing of clumps is 11.30±1.31'(1.36±0.16 pc) and the average spacing of sub-clumps is 7.18±1.19"(0.86±0.14 pc). These spacings agree well with the predicted values of the thermal (0.86 pc) and turbulent sausage instability(1.43 pc) by adopting a cylindric geometry of the ISF with an inclination of 60°with respect to the line of sight. We also find a velocity gradient of about 0.6 km s-1 pc-1 that runs alongthe ISF which likely arises from an overall rotation of the Orion A molecular cloud. The inferred ratio between rotational and gravitational energy is wel below unity. Furthermore, fluctuations are seen in the centroid velocity diagram along the ISF. The OMC-1 to 5 clouds are located close to the local extrema of the fluctuations, which suggeststhat there exist gas flows associated with these clumps in the ISF. The derived NHs(1,1) and(2,2) rotation temperatures in the OMC-1 are about 30-40 K while lower temperatures(below 20 K) are obtained in the northem and southern parts of the ISF. In OMC-2, OMC-3, and the northern part of OMC-4, we find higher temperatures at the boundaries, lower ones in the interior. Finally we introduce the most likely evolutionary scenario for filament fragmentation and understanding the velocity. Then, we study the HIA(Hyperfine Intensity Anomaly) in NHs(1,1). HIA is omnipresent in the molecular cloud, but we still not understand their generation mechanism. Previous HIA studies mostly aimed at single point observations toward star formation regions. However, this may be biased by the different physical and chemical environment. Thus we use the GBT NHa (1,1) data of the ISF to understand the HIA with similar environment. We firstly developed a procedure to calculate the HIA with big survey data and the procedure worked well with the GBT NH,(1,1) data. We find the HIA values of the outer are mostly greater than 1 but the HIA values of the inner satalite lines are smaller than 1. We hope to use our procedure to the ammonia survey project of our group in the future to understand the HIA in the scale of our milk way. Whether high-mass stars form mediated by the disk/outflow system, in a similar way as low-mass stars form, remains a hot topic in the studies of high-mass star fomation. From about 1990s,a number of studies of molecular outflows have been carried out towards a variety of candidates of high mass young stellar object with single dishand interferometric observations. Outflows have been verified to be ubiquitous in highmass star forming regions(SFRs). Naively, if the assumption that disks and outflows are strictly associated is correct as in low-mass SFRs, disks should be widespread in high-mass SFRs. Whereas in reality, only a very few disk candidates have been detected in high-mass SFRs. Furthermore, most of the disk candidates are discovered in the regime of103~10Le. The rare of disks detections, especially in ~105L. SFRs, is an observational bias(short time scale/deep embedding/large distance) or cames from the intrinsic explanations of different physical models to low-mass stars forming,e.g, those involving coalescence of lower mass stars, which is still an open question. Furthermore, we can not give a clear picture of the circumstellar disk around a high-mass star. for example, we still no known some basic parameters such as disk mass, inner and outer radius, height, and rotation curve etc. Moreover, through the disk, we can directly and precisely derive the accretion rate and the physical properties of the central protostar(dynamical mass etc.). Then at～~0.0lpc scale, we conducted VLA, SMA, VLBA studies toward a 1.2x10^5 Le high-mass star formation region, IRAS18360-0537. The source is located at a kinematic distance of 6.3 kpc. It is perhaps the most promising candidate of a high-mass protostar associated with a Keplerian' disk' and a jet/outflow system in the regime of L>105Le. In IRAS 18360-0537, the SMA 1.3 mm continuum map shows two condensations, MlM1 and MM2. Meanwhile the SMA CO and SiO indicate a northeast southwest bipolar outflow centered at MM1 while CH3OH and CH3CN trace a northwest-southeast rotation gradient perpendicular to the out ow axis. Furthermore, CN spectraalso from the SMA, present typical inverse P-Cygni profiles which demonstrate infall motions. We also carried out VLA 3.6 cm,1.3 cm, and 7mm radio continuum observa-tions towards IRAS18360-0537 and the derived IM1 fuses are about 0.42 mJy,1.89 mly, and 4.86 mJy respectively. Combining the SMA and VLA observations, we constructed a Spectral Energy Distribution (SED) of IRAS 18360-0537 MM1. The index of the free-free emissioin is about 1.5. These results indicate that IRAS 18360-0537 is presently in a very early evolutionary stage,e.g in a stage prior to the formation of an HII region Combined with previous VLBA H2O maser observations in BeSSeL project (G026.50+0.28), recently we conducted a VLBA OH, CH, OH, and H2O maser observations towards IRAS 18360-0537. In our preliminary results, the H2O masers seem to associated with the outflow and the outflow may show procession. |
| Pages | 81 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/2483 |
| Collection | 研究生学位论文 |
| Affiliation | 中国科学院新疆天文台 |
| First Author Affilication | Xinjiang Astronomical Observatory, Chinese Academy of Sciences |
| Recommended Citation GB/T 7714 | 吴刚. 猎户座分子云丝条结构太尺度观测研究和大质量恒星形成区IRAS18360-0537的高分辨率观测研究[D]. 北京. 中国科学院大学,2018. |
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| 学位论文-吴刚.pdf（20616KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
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