While collisionally excited lines in HII regions allow one to easily probe the chemical composition of the interstellar medium in galaxies, the possible presence of important temperature fluctuations casts some doubt on the derived abundances. To provide new insights into this question, we have carried out a detailed study of a giant HII region, H 1013, located in the galaxy M101, for which many observational data exist and which has been claimed to harbour temperature fluctuations at a level of t^2 = 0.03-0.06. We have first complemented the already available optical observational datasets with a mid-infrared spectrum obtained with the Spitzer Space Telescope. Combined with optical data, this spectrum provides unprecedented information on the temperature structure of this giant HII region. A preliminary analysis based on empirical temperature diagnostics suggests that temperature fluctuations should be quite weak. We have then performed a detailed modelling using the pyCloudy package based on the photoionization code Cloudy. We have been able to produce photoionization models constrained by the observed Hb surface brightness distribution and by the known properties of the ionizing stellar population than can account for most of the line ratios within their uncertainties. Since the observational constraints are both strong and numerous, this argues against the presence of significant temperature fluctuations in H 1013. The oxygen abundance of our best model is 12 + log O/H = 8.57, as opposed to the values of 8.73 and 8.93 advocated by Esteban et al. (2009) and Bresolin (2007), respectively, based on the significant temperature fluctuations they derived. However, our model is not able to reproduce the intensities of the oxygen recombination lines . This cannot be attributed to observational uncertainties and requires an explanation other than temperature fluctuations.
HeI in the central Giant HII Region of NGC 5253. A 2D observational approach to collisional and radiative transfer effects
NGC 5253是详细研究星暴星系的理想实验室。我们首次在星暴星系中对He^+的碰撞和辐射转移效应的空间行为进行了二维研究。基于用FLAMES和GMOS获得的数据分析HeI系。碰撞效应对于单重态级联跃迁可以忽略不计，而对于三重态级联跃迁则相对重要。特别是，它们可以在Heil 7065生产线中贡献高达20%的通量。辐射转移效应在以超级星团为中心的直径为30秒差距的圆形区域内是重要的。利用6条HeI谱线的消光校正通量、T_e、n_e的实际假设、恒星吸收等效宽度以及最近的发射率，绘制了HeI丰度y^+的分布图。我们发现，在整个地图区域内，平均值为10^3 y^+ ~80.3。激发和总氦丰度y_tot之间的关系与没有丰度梯度一致。在推导He丰度的过程中，所采用的假设占主导地位。我们说明了由于主GHIIR中存在沃尔夫-拉叶星，因此检测推定的He富集的困难。数据是勉强一致的过量的N/He比在N富集区的顺序，大气中的N/He比在WR星和不确定性估计的N/He比。
An In-Depth View of the Mid-Infrared Properties of Point Sources and the Diffuse ISM in the SMC Giant HII Region, N66
本文利用斯皮策空间望远镜的红外光谱仪研究了低金属丰度（~0.2太阳）的巨大HII区N66的中红外点源和弥漫星际介质（ISM）。我们研究了14个有针对性的红外点源，以及光谱的扩散ISM是代表的光解离区域（PDR）和HII区域。在点源光谱，我们光谱确认，最明亮的中红外点源是一个大规模的嵌入式年轻恒星的对象，我们检测到硅酸盐的发射与两个年轻的星团，我们观察到光谱特征的一个已知的B[e]超巨星，更常见的是与赫比格Be星。在漫ISM中，我们提供了额外的证据表明，非常小的颗粒人口被光破坏的硬辐射场。11.3 μ m PAH复合物发射在点源和ISM光谱中都表现出无法解释的质心偏移，应在更高的信噪比和分辨率下进行研究。与其他地区的研究不同，6.2微米和7.7微米波段的通量是解耦的;数据点覆盖了I6.2/I11.3比值的窄带内的I7.7/I11.3 PAH比值的大范围。此外，在PAH电离中存在扩散，在辐射场相对较软的密集PDR中更中性，但在扩散ISM/PDR中电离。相比之下，PAH的尺寸分布似乎是独立的本地电离状态。对于河外低金属丰度恒星形成区尚未解决的研究很重要，我们发现来自红外亮点源的发射仅占整个区域PAH发射的20-35%。这些结果与其他具有类似硬辐射场和强辐射场的恒星形成区域进行了比较。
