天鹅座大质量恒星形成的历史记录
The historical record of massive star formation in Cygnus
摘要：
天鹅座区域，支配着银河系的局部旋臂，是离大质量恒星形成最近的复合体之一。它的大质量恒星成分、正在形成的恒星区域和分子气体已经被详细研究。然而，人们对该地区过去1000万年以来的历史知之甚少。红超巨星的亮度和光谱特征使我们很容易识别它们，并在天鹅座区域建立一个几乎完整的此类恒星样本，从而提供了一个大质量恒星形成的记录，延伸到过去的几十万年，这是一个通过目前可观察到的O和早期B星无法达到的时期。我们在84平方度的区域内选择了一个明亮的红色恒星样本，覆盖了天鹅座区域的整个延伸。我们已经获得了在红色可见光范围内的光谱，可以进行准确，均匀的光谱分类，以及超巨星和其他冷恒星之间的可靠分离。我们的数据得到了盖亚数据发布2天体测量数据的补充。我们已经在该地区确定了29颗红超巨星，其中17颗以前没有被归类为超巨星。29个中的24个最有可能属于天鹅座区域，剩下的4个属于英仙座臂。我们使用它们的光度和质量来推断该区域的恒星形成历史。强烈的大质量恒星形成活动被发现开始于大约1500万年前，我们发现了另外两个事件的证据，一个发生在2000万到3000万年前，另一个结束于大约4000万年前。年轻或年长于2000万年的红超巨星在运动学性质上有微小但显著的差异，暗示年长的恒星群是在现在的天鹅座复合体的前身之外形成的，可能在人马座-船底座臂。
英文摘要：
The Cygnus region, which dominates the local spiral arm of the Galaxy, is one of the nearest complexes of massive star formation. Its massive stellar content, regions of ongoing star formation, and molecular gas have been studied in detail. However, little is known of the history of the region beyond the past 10 Myr. The brightness and spectroscopic characteristics of red supergiants make it easy to identify them and build up a virtually complete sample of such stars at the distance of the Cygnus region, thus providing a record of massive star formation extending several tens of Myr into the past, a period inaccessible through the O and early B stars observable at present. We have made a selection of a sample of bright, red stars in an area of 84 square degrees covering the whole present extension of the Cygnus region. We have obtained spectroscopy in the red visible range allowing an accurate, homogeneous spectral classification as well as a reliable separation between supergiants and other cool stars. Our data are complemented with Gaia Data Release 2 astrometric data. We have identified 29 red supergiants in the area, 17 of which had not been previously classified as supergiants. Twenty-four of the 29 most likely belong to the Cygnus region and four of the remaining to the Perseus arm. We have used their derived luminosities and masses to infer the star formation history of the region. Intense massive star formation activity is found to have started approximately 15 Myr ago, and we find evidence for two other episodes, one taking place between 20 and 30 Myr ago and another one having ended approximately 40 Myr ago. There are small but significant differences between the kinematic properties of red supergiants younger or older then 20 Myr, hinting that stars of the older group were formed outside the precursor of the present Cygnus complex, possibly in the Sagittarius-Carina arm.
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