天鹅座X巨大致密核的碎裂和质量分离
Fragmentation and mass segregation in the massive dense cores of Cygnus X
摘要：
我们目前的Plateau de Bure干涉仪观测获得的连续在1.3和3.5毫米对6个最大规模和年轻的（IR安静）密集的核心在天鹅座X。位于只有1.7千秒差距，天鹅座X区域提供了达到足够小的尺度（1.3毫米的1700天文单位的数量级）的机会，以分离单个塌陷物体。核心被亚碎片化，5个核心内总共有23个碎片。只有最紧凑的核心，CygX-N63，实际上可能是一个单一的大质量原恒星，其包络质量高达60 Msun。其他核心中的碎片的大小和间距与附近原星团中的低质量恒星前和原恒星凝聚相似，并且可能具有相同的性质。在这23个原恒星天体中，有9个可能是OB星的前身，其包层质量从6到23 Msun不等。碎片化的水平是全球高于湍流调节，单片崩溃的情况下，但并不像预期的那样高，在一个纯粹的重力湍流的情况下，质量分布是由低质量的原恒星/恒星。在这里，在高质量碎片中的总核心质量的分数分别在CygX-N12、CygX-N53和CygX-N63中达到高达28%、44%和100%的值，远高于IMF类质量分布所预测的值。碎裂效率的增加作为密度的函数在核心中提出的是由于自重力导致引力坍缩在致密的核心的规模的重要性越来越大。与此同时，核心往往会在其中心区域分裂成几个巨大的原恒星。因此，我们可能在这里目睹了形成中的团簇的原始质量分离。
英文摘要：
We present Plateau de Bure interferometer observations obtained in continuum at 1.3 and 3.5 mm towards the six most massive and young (IR-quiet) dense cores in Cygnus X. Located at only 1.7 kpc, the Cygnus X region offers the opportunity of reaching small enough scales (of the order of 1700 AU at 1.3 mm) to separate individual collapsing objects. The cores are sub-fragmented with a total of 23 fragments inside 5 cores. Only the most compact core, CygX-N63, could actually be a single massive protostar with an envelope mass as large as 60 Msun. The fragments in the other cores have sizes and separations similar to low-mass pre-stellar and proto-stellar condensations in nearby protoclusters, and are probably of the same nature. A total of 9 out of these 23 protostellar objects are found to be probable precursors of OB stars with envelope masses ranging from 6 to 23 Msun. The level of fragmentation is globally higher than in the turbulence regulated, monolithic collapse scenario, but is not as high as expected in a pure gravo-turbulent scenario where the distribution of mass is dominated by low-mass protostars/stars. Here, the fractions of the total core masses in the high-mass fragments are reaching values as high as 28, 44, and 100 % in CygX-N12, CygX-N53, and CygX-N63, respectively, much higher than what an IMF-like mass distribution would predict. The increase of the fragmentation efficiency as a function of density in the cores is proposed to be due to the increasing importance of self-gravity leading to gravitational collapse at the scale of the dense cores. At the same time, the cores tend to fragment into a few massive protostars within their central regions. We are therefore probably witnessing here the primordial mass segregation of clusters in formation.
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