Sequential star formation at the periphery of the HII regions Sh 217 and Sh 219
Sequential star formation at the periphery of the HII regions Sh 217 and Sh 219
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DOI：
10.1051/0004-6361:20021841
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发表时间：
2002-12
期刊：
影响因子：
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通讯作者：
L. Deharveng;A. Zavagno;L. Salas;A. Porras;J. Caplan;I. Cruz-González
中科院分区：
文献类型：
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作者：
L. Deharveng;A. Zavagno;L. Salas;A. Porras;J. Caplan;I. Cruz-González
HII区域Sh 217和Sh 219是由环形光解离区域（PDR）围绕的斯特罗姆格伦球的教科书示例。在21 cm原子氢发射和8微米附近的尘埃（PAH）发射中都观察到环形PDR（MSX Survey）。在Sh 217和Sh 219中，在环形PDR的方向上观察到超紧凑的无线电连续源。JHK的观测显示，在这些射电源的方向上存在着高度红化的星团（AV ~ 20等）。这些星团也是IRAS的来源，Sh 217的光度为22700 Lo，Sh 219的光度为5900 Lo。每个星团都至少包含一颗明亮的星星，并有红外色过剩; Sh 219星团中的恒星有H-α辐射。与Sh 217相关的星团几乎是球形的，在其中心包含发光的天体。与Sh 219相关的团簇沿着该HII区的电离前沿被拉长。我们认为，这些是“第二代集群”，这意味着目前在PDR的物理条件，接近电离前沿，有利于形成包含大质量物体的集群。我们讨论的物理机制，这可能是在所观察到的触发星星形成的起源。
The HII regions Sh 217 and Sh 219 are textbook examples of a Stromgren sphere surrounded by an annular photodissociation region (PDR). The annular PDR is observed in both the 21 cm atomic hydrogen emission and the dust (PAH) emission near 8 micron (MSX Survey). An ultracompact radio continuum source is observed in the direction of the annular PDR, in both Sh 217 and Sh 219. JHKobservations show the presence of highly reddened stellar clusters (AV ~ 20 mag) in the directions of these radio sources. These clusters are also IRAS sources, of luminosities 22700 Lo for Sh 217 and 5900 Lo for Sh 219. Each cluster contains at least one luminous star with an IR colour excess; the one in the Sh 219 cluster shows H-alpha emission. The cluster associated with Sh 217 is almost spherical and contains luminous objects at its centre. The cluster associated with Sh 219 is elongated along the ionization front of this HII region. We argue that these are `second-generation clusters', which means that the physical conditions present in the PDRs, close to the ionization fronts, have favoured the formation of clusters containing massive objects. We discuss the physical mechanisms which may be at the origin of the observed triggered star formation.