天鹅座OB2的郊区
The outskirts of Cygnus OB2
摘要：
我们研究了天鹅座OB 2周围可能存在的早期型恒星扩展晕，这是暗示了近红外色色图，它的关系，天鹅座OB 2本身，以及附近的协会天鹅座OB 9和天鹅座X北复杂的恒星形成区。在目标区域共识别出96颗早型星，占观测样本的近一半。它们中的大多数在现有的分辨率下都具有OB星所期望的无特征的近红外光谱。另外18颗显示Brackett发射线的恒星可以根据它们的红外线过剩分为演化的大质量恒星（最有可能是Be星）和Herbig Ae/Be星。一个与天鹅座OB 9/NGC 6910相关的组成部分被清楚地识别出来，以及天鹅座X北的早期型恒星表面密度的增强。我们还发现了一个领域的人口，主要由早期的B巨星和超巨星，这可能是在最近的研究中确定的天鹅座OB 2周围的内部1度圈相同。这个种群的年龄和大规模的扩展放弃了与天鹅座OB 2或任何其他特定协会的直接关系。早先关于天鹅座OB 2可能超出其中心的大范围的说法，非常巨大的聚集体似乎被我们的发现驳回了。几乎无处不在的演化恒星与大规模的前体的存在表明，天鹅座的大规模恒星形成历史早在该地区目前观察到的OB协会形成之前就已经开始了。
英文摘要：
We investigate the possible existence of an extended halo of early-type stars around Cygnus OB2, which is hinted at by near-infrared color-color diagrams, and its relationship to Cygnus OB2 itself, as well as to the nearby association Cygnus OB9 and to the star forming regions in the Cygnus X North complex. A total of 96 early-type stars are identified in the targeted region, which amounts to nearly half of the observed sample. Most of them have featureless near-infrared spectra as expected from OB stars at the available resolution. Another 18 stars that display Brackett emission lines can be divided between evolved massive stars (most likely Be stars) and Herbig Ae/Be stars based on their infrared excesses. A component associated with Cygnus OB9/NGC 6910 is clearly identified, as well as an enhancement in the surface density of early-type stars at Cygnus X North. We also find a field population, consisting largely of early B giants and supergiants, which is probably the same as identified in recent studies of the inner 1-degree circle around Cygnus OB2. The age and large extension of this population discards a direct relationship with Cygnus OB2 or any other particular association. Earlier claims of the possible large extent of Cygnus OB2 beyond its central, very massive aggregate seem to be dismissed by our findings. The existence of a nearly ubiquitous population of evolved stars with massive precursors suggests a massive star formation history in Cygnus having started long before the formation of the currently observed OB associations in the region.
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