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

通过对发光线恒星的大规模调查，在OB协会中发现了许多年轻恒星。与表观分子云没有关联的年轻恒星可能是在小云中形成的，这些小云是分子物质的残留物。明亮的边缘云(BRCs)是与HII区域直接相关的小分子云，被认为是正在形成恒星的地点。然而，与以前观测到的没有明亮边缘的BOK球体的比较表明，BRCs在伴生的YSO及其星际尘埃质量方面存在着显著的差异。以往的研究主要基于与IRAS点源相关的BRCs目录。我们制定了一个不偏不倚的BRCs目录，并试图对它们进行多波长研究。我们使用了GRISM光谱仪来观测BRCS中的发射线恒星。甚至在与IRAS源无关的BRCs中也发现了几颗发射线恒星。分子谱线作图对于估算BRCs的物理参数具有重要意义。我们在CS J=2-1谱线中观察到35个BRC，在光学薄H^&lt；13&gt；CO^+J=1-0谱线中观察到24个BRCs。BRCS的典型大小和质量分别为0.3pC和10个太阳质量。我们发现了几个值得注意的有趣的BRC。例如，BRC31由三个致密团块组成。BRC38中显示了致密而块状的尾部结构，其头部面向HII区。这个尾部有几个YSO。在BRC14的情况下，H^&lt；13&gt；CO^+团簇在中心发光的IRAS源周围形成了一个致密的壳层。这表明了分子气体与团簇形成活性之间的相互作用。此外，我们挑战了大视场的近红外成像观测，以研究来自YSOs的CTTS和H2喷流，以了解一些BRC的恒星形成历史。尽管如此，还需要更多的讨论和后续工作来澄清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.