KMS of Xinjiang Astronomical Observatory, CAS
| 恒星形成的早期阶段：纤维状云及红外暗云的观测研究和动力学的莱恩-埃姆登方程理论 | |
| Alternative Title | Star formation in early stages:observational studies toward lamentarymolecular cloud and Infrared dark cloudsand theory of dynamic Lane-Emdenequation |
李大磊
| |
| Subtype | 博士 |
| Thesis Advisor | 加尔肯·叶生别克 |
| 2016 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Discipline | 天体物理 |
| Keyword | 分子云 恒星形成的早期阶段 分子谱线 纤维状分子云 红外暗云 莱恩-埃姆登方程 |
| Abstract | 目前，人们对恒星形成早期阶段的物理性质还不是很清楚。然而，它对理解恒星形成的过程至关重要，是当下恒星形成研究的重点课题。首先，从观测上发现纤维状云是分子云中普遍存在的结构，并且分子云中的绝大部分致密云核都位于纤维状云之上。因此，纤维状云是研究分子云核形成机制和早期动力学演化的重要场所。本文中，利用多波段的数据尤其是分子谱线的数据，我们对纤维状云L1482 及内部致密团块的动力学性质做了详细研究。另外，红外暗云是研究大质量恒星/星团形成早期阶段的极好候选体。利用谱线的数据，我们得到了一批红外暗云的距离信息，为进一步研究红外暗云的物理性质打下了坚实的基础。其次，通常认为分子云核的初始条件是处于流体静力学状态。然而，最近从观测上发现分子云在形成恒星之前，分子云在各个不同尺度上都是处于引力塌缩的状态。所以，发展动力学的模型是非常必要的。本文中，我们发展了动力学的莱恩-埃姆登方程，并且利用此动力学方程对经典的星前核Barnard 68进行了拟合。综上，我们从观测和理论两个方面对恒星形成早期阶段的物理性质进行了研究。 首先，通过纤维状云我们研究了分子云团块的形成机制及其早期的动力学状态。 利用KOSMA 3-米望远镜，我们对L1482进行了12CO(2-1) 和(3-2) 的成图观测。另外，我们也使用了青海站13.7-米望远镜的成图数据13CO(1-0) 和赫歇尔空间天文台的远红外数据。我们从纤维状云L1482中证认了23个块。对这23个团块进行了质量和半径关系的分析，发现加利福尼亚分子云的大质量恒星形成是被抑制的，虽然它跟已知的猎户座分子云在质量和尺度上很类似。我们的分析发现纤维状云是热不稳定的，所以分子云团块的形成可能是源于沿着纤维状云的引力塌缩。这些团块不是静态平衡的，而很有可能是处于动力学的演化状态。 其次，我们对一批处于早期的大质量恒星形成区候选体红外暗云进行了谱线观测研究。利用KOSMA 3-米望远镜，我们对117 个红外暗云进行了12CO(2-1) 和(3-2) 的单点观测。利用最新发展的贝叶斯距离计算方法，我们计算了这些红外暗云的距离，并且发现这些源都聚集在外臂，英仙臂，本地臂，人马臂和盾牌臂上。我们计算了填充因子修正的12CO(3-2) 和(2-1) 的积分强度比。对于大部分源，这个比值为0.69 ± 0.47。另外，剩余的少量源具有较高积分强度比可能源于周围HII区的加热效应。含有原恒星和不含原恒星的红外暗云积分强度比没有差别。 最后，我们利用解析的方法发展了描述分子云核极早期演化的动力学方程。在球对称坐标下，基于自相似变换和一般多方的状态方程，我们分析了理想流体力学方程，得到了含有惯性力的莱恩-埃姆登方程。在中心有限边界条件下，我们获得了方程任意n的常数解及n=0和1的非常数解。 我们在原点附近的小尺度上获得了方程的级数解。我们也讨论了方程的数值解。对于天体物理的应用，在中心有限边界条件下，我们利用一般多方的动力学莱恩-埃姆登方程对分子暗云核Barnard 68进行了拟合。相比于静态的模型，我们动力学的解所拟合出来的参数能跟更多的观测事实符合的很好，包括密度，温度和气压。 综上，对于纤维状云L1482，分子云核通过纤维状云的引力塌缩形成，并且它们处于动力学的演化状态。更进一步，我们从理论上发展了动力学的莱恩-埃姆登方程，它也许可以作为描述分子云核极早期演化的一种动力学模型。 |
| Other Abstract | Recently, the star formation in the early stages are poorly understood. However, the early stages of star formation are very important to understand the star formation process. Therefore, it is a critical topic in the star formation field. Firstly, the filamentary molecular clouds are common structure in the molecular clouds from observations and most of the denser cores are located in the filament molecular clouds. Therefore, the filament molecular clouds are very important places for exploring the mechanism of formation of molecular denser cores. Therefore, using multi-wavelength bands data, especially molecular lines data, we investigate the kinematic and dynamical states of L1482 filament and physical properties of dense molecular clumps embedded therein. In addition, Infrared Dark Clouds (IRDCs) are a valuable sample to study the early stages of massive star formation/star clusters formation. In this paper, using molecular data, the distances of some IRDCs were derived. These IRDCs will be important in the future studies. Secondly, molecular clouds at all stages prior to real star formation are always gravitational collapse derived from recently observational data. However, in general, the initial condition of molecular cloud core is hydrostatic state. Therefore, it is important to study the dynamic model. In this paper, we studied the dynamic Lane-Emden equation, and also this dynamic equation was used to fit the classic pre-stellar core Barnard 68. In summary, we explored the early stages of star formation from both observations and theories. Firstly, we investigate the kinematic and dynamical states of this molecular filament and physical properties of several dozens of dense molecular clumps embedded therein. We present and compare molecular line emission observations of the J=2−1 and J=3−2 transitions of 12CO in this molecular complex, using the K¨olner Observatorium fu¨r Sub-Millimeter Astronomie (KOSMA) 3-metertelescope. These observations are complemented with archival data observations and analyses of the 13CO J = 1 − 0 emission obtained at the Purple Mountain Observatory (PMO) 13.7-meter radio telescope, as well as infrared emission maps from the Herschel Space Telescope online archive, obtained with the SPIRE and PACS cameras. We have identified 23 clumps along the molecular filament L1482 in the California molecular cloud. While surprisingly similar in mass and size to the much better known Orion molecular cloud, the formation rate of high-mass stars appears to be suppressed in the California molecular cloud compared with that in the Orion molecular cloud based on the mass-radius threshold derived from the static Bonnor-Ebert sphere. Our analysis suggests that these molecular filaments are thermally supercritical and molecular clumps may form by gravitational fragmentation along the filament. Instead of being static, these molecular clumps are most likely in processes of dynamic evolution. Secondly, using molecular line observations, we explored the IRDCs which are an excellent sample to study the very early stages of evolution of massive star. Using the KOSMA telescope, we performed single point12CO(2-1) and(3-2) observations simultaneously toward 117 IRDCs. The distances of the IRDCs have been calculated using the newly development Bayesian distance estimator indicating that the sources are mainly concentrated in the Outer, Perseus, Local, Sagittarius and Scutum arms. The filling factors are used to correct the integrated intensity ratio of 12CO(3-2) to (2-1) resulting in a typical value of 0.69 ± 0.47 for most of the sources. The remain sources exhibit enhanced values maybe because of the presence of a nearby HII region. The ratios do not show significant differences for sources with embedded far-infrared sources. Finally, using analytic methods, we developed a dynamic equation to modelthe early stage of molecular cloud core. In the self-similar dynamic formulation, we analyze ideal hydrodynamic equations with spherical symmetry using a general polytrophic (GP) equation of state (EoS), and derive the GP dynamic Lane-Emden equation (LEE) with the radial inertial force effect. For the central finite boundary conditions, we obtain an exact constant solution for arbitrary in-dex n and analytic variable solutions for n = 0 and 1. Series expansion solutions are derived near the origin at small radii with the explicit recursion formulae forthe series coefficients for both the GP and isothermal cases. We further obtain numerical solutions with no analytic counterparts. For astrophysical applications, we invoke our GP dynamic LEE with central finite boundary conditions to fit the classic source molecular cloud core Barnard 68 in contrast to the static Bonnor-Ebert sphere; our GP dynamic model fitting parameters appear to be sensibly consistent with the available observations and diagnostics for density, temperature and gas pressure. In summary, for the L1482, the molecular cloud cores are formed from filament molecular cloud under gravitational collapse, and these cores are dynamic evolution. Further, we studied the dynamic Lane-Emden equation to model the early stages of cold cores. |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/1716 |
| Collection | 研究生学位论文 射电天文研究室 |
| Affiliation | 中国科学院新疆天文台 |
| Recommended Citation GB/T 7714 | 李大磊. 恒星形成的早期阶段：纤维状云及红外暗云的观测研究和动力学的莱恩-埃姆登方程理论[D]. 北京. 中国科学院大学,2016. |
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| 李大磊-学位论文.pdf（6777KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
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