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星协中发现了许多年轻的恒星。与明显分子云无关的年轻恒星可能是在小的分子云中形成的，这些小分子云是分子物质的残余。边缘云（BRC），与HII区域直接相关的小分子云，被认为是正在进行的星星形成的场所。然而，与先前观测到的没有明亮边缘的博克球状体的比较表明，BRC在相关的YSO的热光度和它们的星周尘埃质量方面有显着差异。以往的研究主要是基于与IRAS点源相关的BRC目录。我们做了一个无偏的BRCs目录，并试图对它们进行多波长研究。我们用棱镜摄谱仪测量了BRC中的发射线星。甚至在BRC中也发现了几颗发射线星，它们与IRAS源无关。分子谱线作图对于估算BRC的物理参数具有重要意义。我们在CS J=2-1谱线上观测到35个BRC，在光学薄的H^<13>CO^+ J=1-0谱线上观测到24个BRC。BRC的典型大小和质量分别为0.3 pc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，BRC 31由三个致密团块的聚集体组成。BRC 38中显示了密集和丛生的尾部结构，其头部朝向HII区。这个尾部有几个YSO。在BRC 14的例子中，H^<13>CO^+团簇在中心发光的IRAS源周围形成了致密的壳层。这表明分子气体和团簇形成活动之间的相互作用。此外，我们对宽视场近红外成像观测提出了挑战，以研究来自YSO的CTT和H2喷流，以了解某些BRC的星星形成历史。然而，需要更多的讨论和后续工作来澄清BRC在星星形成中的作用。

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.