Study of star formation in the small molecular clouds associated with HII regions

通过对发射线星的大规模巡天，在OB星团中发现了许多年轻恒星。有一种可能是，与明显的分子云无关的年轻恒星是在小云中形成的，这些小云是分子物质的残余。明亮边缘云（BRCs）是与HII区域直接相关的小分子云，被认为是正在进行的恒星形成的场所。然而，与先前没有明亮边缘的Bok球状体的观测结果的比较表明，BRCs在相关yso的热光度和它们的星周尘埃质量方面存在显著差异。以往的研究主要基于与IRAS点源相关的BRCs目录。我们制作了一个无偏的BRCs目录，并尝试对它们进行多波长研究。我们使用光栅光谱仪对BRCs中的发射线星进行了测量。甚至在与IRAS源无关的BRCs中也发现了一些发射线星。分子线定位对BRCs的物理参数估计具有重要意义。我们在CS J=2-1系中观察到35个BRCs，在光学薄的H^<13>CO^+ J=1-0系中观察到24个BRCs。brc的典型大小和质量分别为0.3个太阳质量和10个太阳质量。我们发现了几个有趣的BRCs。例如，BRC31由三个密集团块的聚集组成。BRC38尾部结构致密块状，头部面向HII区。这个尾部有几个yso。在BRC14的情况下，H^<13>CO^+团块在中央发光IRAS源周围形成了致密的壳层。这表明分子气体与星团形成活动之间存在相互作用。此外，我们还挑战了宽视场的近红外成像观测，研究了来自yso的ctt和H2射流，以了解一些BRCs的恒星形成历史。然而，需要更多的讨论和后续工作来阐明BRCs在恒星形成中的作用。

Many young stars were found in OB associations by the large-scale survey of emission-line stars. It is possible that the young stars not associated with apparent molecular clouds have formed in small clouds, which are remnants of molecular material. Bright-rimmed clouds (BRCs), small molecular clouds directly associated with HII regions, are believed to be sites of ongoing star formation. However, the comparisons with previous observations of Bok globules without bright rims indicated that BRCs differ significantly in the bolometric luminosities of associated YSOs and their circumstellar dust mass. Previous studies are mainly based on the catalog of BRCs associated with IRAS point sources. We made an unbiased catalog of BRCs, and tried to perform multi-wavelength studies of them. We used the grism spectrograph to survey emission-line stars in BRCs. Several emission-line stars are found even in BRCs, which are not associated with IRAS sources. Molecular line mapping is important to estimate the physical parameters of BRCs. We observed thirty-five of BRCs in CS J=2-1 line, and twenty-four of them in optically thin H^<13>CO^+ J=1-0 line. The typical size and mass of BRCs are 0.3 pc and 10 solar masses, respectively. We found several interesting BRCs to note. For example, BRC31 consists of the aggregation of three dense clumps. The dense and clumpy tail structure is shown in BRC38, whose head part is facing towards the HII region. This tail part harbors several YSOs. In the case of BRC14, H^<13>CO^+ clumps make a dense shell around the central luminous IRAS source. This suggests the interaction between the molecular gas and the cluster forming activity. Furthermore, we challenged the NIR imaging observations of wide field of view to investigate CTTs and H2 jets from YSOs to understand the star forming history of some BRCs. Still, more discussions and follow-up works are needed to clarify the role of BRCs in star formation.