KMS of Xinjiang Astronomical Observatory, CAS
| 大质量恒星形成区（红外bubble和猎户座星云）的连续谱和分子谱线研究 | |
| Alternative Title | Continuum and Molecular Line Studies in Massive Star Formation Regions (the Infrared Bubble and the Orion Molecular Cloud) |
周冬冬
| |
| Subtype | 博士 |
| Thesis Advisor | 加尔肯·叶生别克 ; 周建军 |
| 2020 | |
| 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,bubble,精细结构异常,年轻星,云块 |
| Abstract | 大质量恒星的形成研究是分子云、星系研究乃至宇宙学研究的重要课题。为了更好地理解大质量恒星形成和演化过程，首先需要了解母体分子云是如何塌缩形成大质量恒星的，然后还需要研究其对周围环境的反馈作用及其对周围恒星形成活动的影响。理解这两方面的内容对我们全面认识恒星形成和演化至关重要。近几十年来，随着射电和红外天文学的迅猛发展，大质量恒星形成和大质量恒星对其周围环境的反馈研究取得了一些进展，也存在很多问题。因此我们通过bubble 和猎户座分子云研究进一步了解大质量恒星对周围分子云环境的反馈作用及其对恒星形成活动的影响。Bubble 有一个成长发育的过程，研究bubble在成长过程中与周围分子云环境及恒星形成情况将可能给出触发恒星形成更为可靠的证据。基于此目的，我们希望通过对不同尺度的bubble 进行大样本研究来实现。我们首先挑选了样本中典型的大尺度和小尺度bubble G15.684-0.29 和N13进行多波段研究。G15.684-0.29是一个半径为15.7 pc的红外bubble，其大小表明它有足够的时间触发恒星形成。首先，我们利用Hi-GAL数据开展G15.684-0.29周围的尘埃研究，证认了39个尘埃云块，这些云块满足形成大质量恒星的条件，且大部分云块位于bubble的壳层上。其次，利用JCMT的12CO(J = 3 → 2) 数据进行了分子云环境研究，证认了19 个分子云块，这些分子云块都处于引力束缚状态。第三，在bubble周围证认了9个Class I年轻星（Young stellar object，YSO）, 28个Class II YSO和12个Transition Disk（TD）。最后，估算bubble在湍动物质中的动力学年龄约为4.0 Myr，碎裂年龄为0.82 ± 1.74 Myr。显然，动力学年龄明显大于碎裂年龄，因此推断G15.684-0.29扩张触发恒星形成的主要物理机制是扫集和塌缩模型。但是，不能排除辐射驱动压缩模型对某些YSO 的形成起作用的可能性。另外，我们还证认了5 个O 型星，这些O 型星可能是bubble的激发星。正如所预期的，大尺度bubble的动力学年龄要大得多，但仍然很难找到更有说服力的证据来证明它触发恒星。我们利用多波段数据对小尺度bubble N13触发恒星形成进行研究。首先，利用Hi-GAL、ATLASGAL 及COHRS数据在N13的壳层上证认了3个尘埃云块，7个分子云块。根据云块的表面密度和质量-尺度关系，推断这些云块内部可能正在形成恒星，其中有两个可能正在形成大质量恒星。其次，在N13附近的GLIMPSE、2MASS 和WISE点源目录中开展了YSO证认工作，但是没有证认到YSO。另外，我们还证认了N13空腔内的4 个O型星，它们可能是N13的激发星。最后估算N13的动力学年龄和碎裂年龄分别为0.40 ± 0.49 Myr 和1.14 ± 2.47 Myr。通过比较N13的动力学年龄和碎裂年龄，推断在这个阶段N13触发恒星形成的可能的主要机制是辐射驱动压缩机制。氨分子（NH3）是常用的分子云和恒星形成区的研究探针。在局部热动平衡下，基态的NH3（1,1）线的两条内卫星线和外卫星线应有相等的强度。但是，卫星线强度不等（hyperfine intensity anomaly，HIA）的现象在恒星形成区中普遍存在，但其产生机制还不是很清楚。在模型上，HIA的产生机制目前主要分为致密核（core）模型和系统性的塌缩和膨胀（collapse or expansion，CE）模型。如果HIA的主要产生机制是core模型的话，观测结果可以作为大质量恒星通过竞争吸积模型形成的观测证据。如果HIA的产生机制是CE模型的话，氨分子可以成为示踪分子云吸积或者膨胀运动的更好的探针。基于此目的，我们对猎户座的Orion A分子云的积分HIA进行了系统研究，首次提出用内卫星线（inner satellite lines，ISL）和外卫星线（outer satellite line，OSL）的积分强度比来定义HIA（积分HIA），并开发了新的计算程序。Orion A分子云的积分HIA分布没有明显的差异，ISL和OSL的积分HIA中值分别是0.96 ± 0.003 和1.422 ± 0.008，这个结果和致密核模型是一致的，和系统膨胀或塌缩模型是不一致的。我们将积分HIA与NH3的柱密度（N(NH3)）、动力学温度（TK）、固有速度弥散（σV）和非热色散（σNT）进行比较，发现ISL和OSL的积分HIA几乎与N(NH3) 无关，ISL的积分HIA 与TK 成反比，OSL的积分HIA几乎与TK无关。随着TK增大，ISL的积分HIA随着减小，但变得更加异常。结果，积分HIA与σV和σNT 成反比。随着σV 和σNT的增加，ISL的积分HIA值逐渐降低，而OSL的积分HIA值变为1（没有异常）。这些相关性不能用HIA core模型来解释，但可以用CE模型来解释。这个结果得到的一些属性可以由core模型解释，而其他属性可以由CE模型解释，因此两者的结合才能解释所有测量的HIA分布。 |
| Other Abstract | Massive star formation is basis to the studies of molecular clouds, galaxies, and our universe. For better understanding it, firstly we should know how to make a high massive star in its natal molecular cloud, and then we should understand how does the young stellar object impact on the molecular cloud and second generation star formation through their feedback. In past decades, thanks to the development in radio and infrared astronomy, there are many progresses have been made in massive stars formation and the feedback studies. In the same time, there are still many open questions need to be addressed. We hope to study on bubble and the Orion Molecular Cloud to understand the feedbacks of massive stars to the surroundings, and the effects on the stellar formation of parent molecular clouds.Bubble is growing up all the time. Studies of the interaction between bubble and surrounding material and the star formation of bubble may obtain more reliable evidences for triggering star formation. We plan to study a lot of bubbles with different scale try to do that. Firstly, we do a study of the typical large-scale and small-scale bubble G15.684-0.29 and N13 with multi-wavelength analysis respectively.The bubble G15.684-0.29 has a radius of 15.7 pc, the large size indicates it may have enough time to trigger star formation. We identify 39 dense cold clumps around the bubble from Hi-GAL survey, all of them satisfy the criteria forming massive stars, and most of them lie in the bubble shell. We identify 19 molecular clumps around the bubble from JMCT 12CO(J = 3 → 2) survey, all of them are gravitationally bound. We found 9 Class I YSOs, 28 Class II YSOs and 12 Transition Disks (TDs) around the bubble. The dynamical age of G15.684-0.29 in a turbulent medium is _ 4 Myr, which is much greater than the shell fragmentation time 0.82 ± 1.74 Myr. We tend to suggest that triggered star formation may be ongoing in the shell of the bubble, and the collect & collapse (C&C) model may work here, but we cannot rule out the possibility the radiation-driven implosion (RDI) model may work on the formation of some YSOs. We find 5 O stars that may be exciting the bubble. As we expected, the larger bubble has a much longer dynamical age, but it is still difficult to find more compelling evidences for triggered star formation.According to the multi-wavelength analysis, we present a study on the environment and star formation of the little bubble N13. We identified 3 dust clumps, and 7 molecular clumps around the bubble from Hi-GAL, ATLASGAL and COHRS survey, respectively. According to the surface densities and mass-size relationship of the clumps it can be infer that the interiors of clumps may be in the process of forming stars, and two of them may be for massive stars formation. YSOs had not been found around N13 although we focus on GLIMPSE, 2MASS and WISE source catalog. In addition, we study on the exciting stars, and identified 4 O stars inside N13. We obtain the dynamical age and fragmentation time of N13 is 0.40 ± 0.49 Myr and 1.14 ± 2.47 Myr, respectively. By comparing the two physical parameters we suggest that RDI model play an important role of triggered star formation in the phase of N13.Ammonia (NH3) is a commonly used tracer in studies of Molecular Clouds (MCs) and star formation regions. In Local Thermodynam-ical Equilibrium (LTE), the two inner satellite lines (ISLs) and the two outer satellite lines (OSLs) of NH3 (1,1) are each predicted to have symmetric, i.e. equal intensities. However NH3 (1,1) spectra, i.e. hyperfine intensity anomalies (HIAs), are observed to be omnipresent in star formation regions, which is still not fully understood.In analytical and numerical calculations, the HIA can be reproduced by non-LTE populations induced by trapping of selected hyperfine transitions in the rotational lines of NH3 connecting the (J,K) = (2,1) and (1,1) inversion doublets. An alternative scenario involves systematic motions like expansion and contraction.If the former mechanism causes the HIA, the emitting cloud should be composed of several small cores with line widths of about 0.3-0.6 km/s (hereafter core model), since clouds with larger line widths would reshuffle the non-thermal populations. Based on this mechanism, the HIA emitting clouds should be composed of many small (10-2pc), high density (106 - 107 cm-3) clumps of 0.3 - 1 Msun , which is further interpreted as being compatible with the ”competitive accretion” model of high-mass star formation. In the latter case, (systematic) collapse or expansion (CE), e.g. outflow, infall, and/or rotation in clouds, could lead to HIAs (hereafter CE model). Photons emitted from one hyperfine transition can be absorbed by another one due to systematic motions resulting in severe changes in the level populations of the NH3 (1,1) sub-levels. Based on this mechanism, the HIA can be used as a better infall/expansion tracer.In addressing this issue, we found that the computation method of the HIA by the ratio of the peak intensities may have defects, especially when being used to process the spectra with low velocity dispersions. Therefore we define the integrated HIAs of the ISLs and OSLs by the ratio of their redshifted to blueshifted integrated intensities (unity implies no anomaly) and develop a procedure to calculate them. Based on this proce dure, we present a systematic study of the integrated HIAs of the ISLs and OSLs in the northern part of the Orion A MC for the first time. We find that integrated HIAs of the ISLs and OSLs are all commonly present in the Orion A MC and no clear distinction is found at different locations of the MC. The medians of the integrated HIAs of the ISLs and OSLs are 0.96 ± 0.003 and 1.422 ± 0.008 respectively, which is consistent with the HIA core model and inconsistent with the collapse or expansion (CE) model. The integrated HIAs of the ISLs and the OSLs are all distributed on both sides of unity, which is inconsistent with the core model but can be explained by the CE model. We compare the integrated HIAs with the para-NH3 column density(N(NH3)), kinetic temperature (TK), total velocity dispersion (σV), and non-thermal velocity dispersion(σNT). The integrated HIAs of the ISLs and OSLs are almost independent of N(NH3). The integrated HIA of the ISLs is inversely proportional to TK and the integrated HIA of the OSLs is almost independent of TK. As TK increases, the integrated HIA of the ISLs, while decreasing, is shifting away from unity, thus line ratios are becoming more anomalous. Finally, the integrated HIAs are inversely proportional to σV and also to σNT. As σV and σNT increase, the integrated HIA of the ISLs is becoming lower, i.e. shifting away from unity, as in the case of TK, while the integrated HIA of the the OSLs decreases to unity (no anomaly). These correlations can not be explained by the HIA core model, but can be explained by the CE model. Thus, some of the properties we find can be explained by the core model and others by the CE model. Apparently only a mixture of both can provide an explanation for all of the measured NH3 anomalies. |
| Pages | 92 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/4144 |
| 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 | 周冬冬. 大质量恒星形成区（红外bubble和猎户座星云）的连续谱和分子谱线研究[D]. 北京. 中国科学院大学,2020. |
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| 周冬冬.pdf（13851KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
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