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arXiv 1909.03809astro-ph.SRastro-ph.GA
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盖亚对天鹅座OB2和船底座OB1两个OB协会的看法:它们形成过程的签名

A Gaia view of the two OB associations Cygnus OB2 and Carina OB1: The signature of their formation process

Beomdu Lim, Yael Naze, Eric Gosset, Gregor Rauw

摘要:

OB星协是星系中主要的恒星形成场所。然而,这些恒星系统的详细形成过程仍然是一个谜。在这种情况下,识别子结构的存在可能有助于追踪其形成过程的足迹。在这里,我们提出了一个运动学研究的两个大规模的OB协会天鹅座OB 2和船底座OB 1使用精确的天体测量从盖亚数据发布2和径向速度。从恒星的星表可以确认这些OB星协是真正的恒星系统。天鹅座OB 2和船底座OB 1都是由几个稠密的星团和一个晕组成,它们具有不同的运动学性质:星团占据的区域直径为5-8秒差距,自行时的色散较小,而晕的自行色散则大2-3倍,直径达数十秒差距。这让人想起与湍流有关的分子云的所谓“线宽-尺寸”关系。考虑到运动学和结构特征是从它们的出生云继承的,这意味着OB星协的形成可能是由超音速湍流驱动的结构形成造成的,而不是由单个嵌入星团的动力学演化造成的。

英文摘要:

OB associations are the prime star forming sites in galaxies. However the detailed formation process of such stellar systems still remains a mystery. In this context, identifying the presence of substructures may help tracing the footprints of their formation process. Here, we present a kinematic study of the two massive OB associations Cygnus OB2 and Carina OB1 using the precise astrometry from the Gaia Data Release 2 and radial velocities. From the parallaxes of stars, these OB associations are confirmed to be genuine stellar systems. Both Cygnus OB2 and Carina OB1 are composed of a few dense clusters and a halo which have different kinematic properties: the clusters occupy regions of 5-8 parsecs in diameter and display small dispersions in proper motion, while the halos spread over tens of parsecs with a 2-3 times larger dispersions in proper motion. This is reminiscent of the so-called "line width-size" relation of molecular clouds related to turbulence. Considering that the kinematics and structural features were inherited from those of their natal clouds would then imply that the formation of OB associations may result from structure formation driven by supersonic turbulence, rather than from the dynamical evolution of individual embedded clusters.

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