Sh 2-307 HII区域的SOAR-OSIRIS观测：太阳圈以外的触发恒星形成
SOAR-OSIRIS observations of the Sh 2-307 HII region: Triggered star formation beyond the solar circle
摘要：
本工作旨在研究Sh 2-307 HII区及相关的恒星星族。Sh 2-307方向的近红外成像和光谱观测是使用SOAR望远镜的OSIRIS进行的。从星团中最亮源的J-、H-和K-波段光谱，我们得出结论，它具有与O 9v-O 9.5v星一致的近红外光谱。使用衍生的光谱类型和各自的J，H和K波段测光，我们计算出的日心距离为3.2（0.5）千秒差距，其中R 0 = 8千秒差距，使这个集群在超过10千秒差距从银河系中心。从Brg，H2和连续窄带图像，我们能够检测到相关的HII区域的近红外对应物，以及电离和冷分子气体之间的界面。使用5 GHz的连续通量密度从PMN目录和Brg窄带图像，我们估计，HII区域的平均直径为0.94（0.15）pc，平均电子密度为550 cm-3和估计的动力学年龄为1.6 Myears年。大部分的源在2微米处呈现出过量的发射，这表明恒星星族非常年轻，许多源仍处于前主序星的吸积阶段。通过使用理论的前主序星轨道，我们得出一个集群的平均年龄约为2.5 Myears，并从分析的分数作为其空间分布的函数，我们发现的嵌入式前主序星恒星星族的年龄分布的证据。最后，通过对低质量源相对于主星团源的空间分布以及与之相关的光解离区的研究，我们得出结论：O型星可能是该区域恒星形成过程的触发源。
英文摘要：
This work aims to the study of the Sh 2-307 HII region and related stellar population. Near-infrared imaging and spectroscopic observations in the direction of Sh 2-307 were performed using OSIRIS at SOAR Telescope. From J-, H- and K-band spectra of the brightest source in the cluster, we conclude that it has a near-infrared spectra compatible with that taken for O9v-O9.5v stars. Using the derived spectral type and the respective J, H and K-band photometry, we compute a heliocentric distance of 3.2(0.5) kpc, which for R0 = 8 kpc, puts this cluster at more than 10 kpc from the Galactic centre. From the Brg, H2, and continuum narrow-band images we were able to detect both the NIR counterpart of the associated HII region, as well as, the interface between the ionised and the cool molecular gas. Using the 5 Ghz continuum flux density taken from the PMN catalogue and the Brg narrow band image we estimate that the HII region has a mean diameter of 0.94(0.15) pc, mean electron density of 550 cm-3 and an estimated dynamical age of 1.6 Myears years. The large fraction of sources presenting excess emission at 2micron suggests that the stellar population is very young, with many sources still in the pre-main sequence accreting phase. By the use of theoretical pre-main sequence tracks we derived a cluster mean age of about 2.5 Myears, and from the analyses of the fraction of excess emission sources as a function of their spatial distribution we found evidence for an age spread for the embedded pre-main sequence stellar population. Finally, from the study of the spatial distribution of the low-mass sources relative to the main-cluster source and associated photo-dissociation zones, we conclude that the O-type star probably has been triggering the star formation process in the region.
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