KMS of Xinjiang Astronomical Observatory, CAS
| 大质量恒星形成区演化阶段的化学研究 | |
| Alternative Title | The global chemical properties of high-mass star forming clumps at different evolutionary stages |
张延军
| |
| Subtype | 硕士 |
| Thesis Advisor | 周建军 |
| 2016 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Discipline | 天体物理 |
| Keyword | 天体化学 分子云 分子 丰度 恒星形成 |
| Abstract | 我们从MALT90 (Millimetre Astronomy Legacy Team 90 GHz)2012个源的巡天数据中，一共选取了197个孤立的大质量恒星形成区的源，同时我们选择了N2H+ (1–0) , HCO+ (1–0) , HCN (1–0) , and HNC (1–0) 四种分子进行研究。研究结果表明积分强度比I(HCO+)/I(HNC), I(HCN)/I(HNC), I(N2H+)/I(HCO+),和 I(N2H+)/I(HCN) 可以很好地示踪大质量恒星形成与演化。但是积分强度比对周围的O/B型星比较敏感。而周围延展的20 cm 的连续辐射可以很好地表明O/B型星的存在。我们发现对于周围没有20 cm 的连续辐射源， I(HCN (1–0) )/I(HNC (1–0) ), I(N2H+ (1–0) )/I(HCN (1–0) ), 和 I(HCO+ (1–0) )/I(HNC (1–0) )可以很好地示踪大质量恒星的演化， I(HCO+ (1–0) )/I(HCN (1–0) ) 和 I(N2H+ (1–0) )/I(HCO+ (1–0) )可以很好地将前prestellar (stage A)和原恒星protostellar(stage B)、 HII/PDR区(stage C)区别开来。另外，我们发现N2H+, HCO+, HCN,和 HNC 的柱密度和丰度都随着演化阶段呈现递增的趋势。丰度比X(HCO+)/X(HNC), X(HCN)/X(HNC), X(N2H+)/X(HCO+) 可以很好地示踪大质量恒星的演化阶段。同时，我们也发现丰度比对周围的O/B型星比较敏感，对于周围没有20 cm 的连续辐射源， X(N2H+)/X(HCO+) 和X(HCO+)/(HNC) 可以很好地示踪大质量恒星的演化， X(HCN)/X(HNC) 可以很好地区分stage A， stage B和stage C. 最后，我们也研究了各个旋臂上的化学特性，但是结果与前面的研究略有不同，造成结果不同的很大原因可能是每个旋臂上的源较少引起的。对于分布在Sagittarius 和Norma-Outer 旋臂上的源，分别有两部分组成，其中一部分靠近银心，另外一部分远离银心。通过比较这两部分源的性质，我们发现靠近银心的源比较年轻，这可能是由于在银心周围分布着比较密的气体，会诞生更多的大质量恒星。 |
| Other Abstract | A total of 197 relatively isolated high-mass star forming clumps were selectedfrom the Millimetre Astronomy Legacy Team 90 GHz (MALT90) survey data and theirglobal chemical evolution were investigated using four molecular lines, N2H+ (1–0) ,HCO+ (1–0) , HCN (1–0) , and HNC (1–0) . The results suggest that the global averaged integrated intensity ratios I(HCO+)/I(HNC), I(HCN)/I(HNC), I(N2H+)/I(HCO+),and I(N2H+)/I(HCN) are promising tracers for evolution of high-mass star formingclumps. However, these ratios are sensitive to the influences of nearby O/B stars.Extended 20 cm continuum emission near the clumps appears to be a good indicator of existing O/B stars. For high-mass star forming clumps that do not coincidewith extended 20 cm continuum emissions, I(HCN (1–0) )/I(HNC (1–0) ), I(N2H+ (1–0) )/I(HCN (1–0) ), and I(HCO+ (1–0) )/I(HNC (1–0) ) were suitable to trace the clumpevolution, with I(HCO+ (1–0) )/I(HCN (1–0) ) and I(N2H+ (1–0) )/I(HCO+ (1–0) ) suitable for distinguishing clumps in prestellar (stage A) from those in protostellar (stageB) and HII/PDR region (stage C). The global averaged column densities and abundances of N2H+, HCO+, HCN, and HNC increase as clumps evolve. The global averaged abundance ratios X(HCO+)/X(HNC), X(HCN)/X(HNC), X(N2H+)/X(HCO+)are also possible evolution tracers. O/B stars nearby the clump also influence the abundance ratios between these four lines. For the clumps that do not coincide with extended 20 cm continuum emissions, X(N2H+)/X(HCO+) and X(HCO+)/(HNC) were suitable for distinguishing clumps in stage A from those in stages B and C, X(HCN)/X(HNC)was suitable for distinguishing clumps in stages A and B from those in stage C. We also studied the chemical properties of the target high-mass star-forming clumps in eachspiral arm of the Galaxy, and got results very different from those above. This is probably due to the relatively small sample in each spiral arm. For high-mass star-formingclumps in Sagittarius arm and Norma-Outer arm, comparing two groups located onone arm with different Galactocentric distances, the clumps near the Galactic centerappear to be younger than those far from the Galactic center, which may be due tomore dense gas concentrated near the Galactic center, and hence more massive stars being formed there. |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/1728 |
| 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 | 张延军. 大质量恒星形成区演化阶段的化学研究[D]. 北京. 中国科学院大学,2016. |
| Files in This Item: | ||||||
| File Name/Size | DocType | Version | Access | License | ||
| 张延军-毕业论文.pdf（18020KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.
Edit Comment