猎户座棒状光子主导区尘埃致密气体的研究

发布时间：2018-02-27 12:40

本文关键词： 星际介质:观测目标(猎户座棒状光子主导区) 星际介质:动力学过程星际介质:致密云团星际介质:分子技术:高分辨率、高谱分辨率观测恒星:恒星形成　出处：《南京大学》2017年硕士论文　论文类型：学位论文

【摘要】：我们首次给出亚毫米波射电干涉仪(the Submillimeter Array,SMA)在猎户座棒状(OrionBar)光子主导区(photon-dominatedregion,PDR)尘埃致密云核的高分辨率观测结果,包括1.3毫米尘埃连续辐射谱,光薄多重跃迁H2CS(6-5)谱线,以及高谱分辨率C34S(4-3)谱线的观测。从1.3毫米尘埃连续辐射谱,我们首次在空间上发现九个可以分辨出来的小尺度(0.01-0.02pc)尘埃致密云核,计算出其质量约为0.02-0.24M⊙之间,其氢分子数密度在3.6 × 105-1.9 × 106 cm-3之间,我们的结果首次从观测上确定了致密成分的确存在于Orion Bar中,验证了长久以来对于Orion Bar的确存在小尺度致密成分的猜想。我们同样首次在Orion Bar中探测到H2CS分子谱线,两条para-H2CS(60,6-50,5)和(62,4-52,3)集中在质量最大的两个致密云核,我们利用这两条首次发现的谱线,在假设局部热动平衡的情况之下,估算致密云核的动力学温度大约在96 K。高谱分辨率的C34S(4-3)分子谱线给出云团的非热速度弥散在0.19-0.54 km s-1之间,这个数值小于气体的热运动(0.59 km s-1),意味着致密云核处在次声速的物理环境之下。我们发现,致密云核的质量均远远小于维里质量和Bonnor-Ebert(BE)质量,意味着它们其实是非维里化状态,同时,也意味在理论上预测,这些云团并不会发生引力坍缩而形成恒星。若在更强烈的远红外光子的辐射下(Far-Ultraviolet,FUV),致密云核有可能从原先稳定存在的状态进行不同的演化阶段,这取决于致密云核的最初柱密度、FUV辐射场强度、最初所处的物理环境以及致密云核的本质属性。如果致密云核是因为湍动汇集而形成的暂时性密度涨落,我们发现其在强烈的FUV辐射下会经历一个激波压缩的过程,但密度升高的程度却不能触发其引力不稳定而塌缩形成恒星。如果致密云核是被云团间介质压力束缚下的物理实体,致密云核质量在FUV辐射场的影响下将会损失5-50%的最初气体质量,但致密云核会在其热壳层与FUV辐射场平衡状态下,保留其中心质量,与热壳层、云团间介质维持压强平衡状态,更难以塌缩形成恒星。我们在估算致密云核质量的过程,动力学温度和尘埃光学不透明度指数都有着一定的不确定性。深场的H2CO/H2CS谱线观测以及多波段的尘埃连续谱观测可以让我们更加准确地确定这两个物理量,也能让我们对Orion Bar中的致密云核演化情况有一个更为准确的判断。总而言之,我们这次研究,不仅首次观测到Orion Bar在小尺度上的致密成分,而且理论计算的所有结果都在预示着这些Orion Bar里的尘埃致密云核并不会在FUV辐射场的影响下演化形成恒星。这个结果,第一次从观测上回答猎户座棒状光子主导区的致密成分是否存在恒星形成活动的问题。
[Abstract]:We present for the first time the high-resolution observations of the dense cloud nuclei of dust in the photonic dominant region of Orion Baron (Orion Baron) by the submillimeter wave radio interferometer (Submillimeter Arrayn SMA), including the 1.3mm continuous dust emission spectrum and the thin and multiple gravimetric transition H2CS6-5) lines. And the observation of the high spectral resolution C34SU 4-3) spectral line. From the 1.3mm dust continuous radiation spectrum, we found for the first time in space nine discernible small scale (0.01-0.02pcc) dust dense cloud nuclei, the mass of which is calculated to be about 0.02-0.24M _ (-). The molecular number density of hydrogen is in the range of 3.6 脳 105-1.9 脳 10 ~ 6 cm-3. Our results show for the first time that the dense component exists in Orion Bar for the first time. It has been proved that there is a small scale dense component in Orion Bar for a long time. We have also for the first time detected the H2CS molecular spectral lines in Orion Bar, two para-H _ 2CS _ (606-50 ~ (5)) and a ~ (6224-52) ~ (3)) are concentrated on the two dense cloud nuclei with the highest mass. On the assumption of local thermodynamic equilibrium, we estimate that the kinetic temperature of dense cloud nuclei is about 96k.High spectral resolution C34Sl4-3) the non-thermal velocity dispersion of cloud clusters is between 0.19-0.54 km / s ~ (-1). This is less than the thermal movement of the gas, 0.59 km / s ~ (-1), which means that the dense cloud nucleus is in the physical environment of subsonic velocity. We find that the mass of the dense cloud nucleus is much smaller than that of the Very mass and the Bonnor-EbertBebe mass, which means that they are in a non-virified state. It also means that it is theoretically predicted that these clouds will not collapse into stars by gravitational collapse. If they are exposed to more intense far-infrared photons, the dense cloud nuclei may undergo different stages of evolution from their previously stable states. This depends on the intensity of the initial column density and FUV radiation field of the dense cloud nucleus, the initial physical environment and the essential properties of the dense cloud nucleus. We found that it experienced a shock compression process under intense FUV radiation, but the increase in density did not trigger its gravitational instability and collapse to form a star. If the dense cloud nucleus is a physical entity bound by the pressure of the intercloud medium, The mass of dense cloud nuclei will lose 5-50% of the initial gas mass under the influence of the FUV radiation field, but the dense cloud nuclei will retain their central mass in the equilibrium state of the hot crust and the FUV radiation field, and maintain the pressure equilibrium state with the hot crust and the medium between the cloud clusters. It's harder to collapse into stars. We're estimating the mass of dense cloud nuclei, Both the kinetic temperature and the opacity index of dust are uncertain. The deep field H2CO / H2CS spectral line observation and the multi-band dust continuous spectrum observation can help us to determine these two physical quantities more accurately. It also allows us to have a more accurate assessment of the evolution of dense cloud nuclei in Orion Bar. In summary, we have not only observed the compact components of Orion Bar on a small scale for the first time in this study. And all the theoretical calculations indicate that the dense cloud nuclei in the Orion Bar do not evolve into stars under the influence of the FUV radiation field. For the first time, the question of whether the dense components of Orion rod-shaped photonic dominant region are active in star formation is answered from observations for the first time.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P151

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