论文标题

NGC 7000/IC 5070复合物中出现恒星关联的形成:恒星和气体的运动分析结果

The Formation of a Stellar Association in the NGC 7000/IC 5070 Complex: Results from Kinematic Analysis of Stars and Gas

论文作者

Kuhn, Michael A., Hillenbrand, Lynne A., Carpenter, John M., Menendez, Angel Rodrigo Avelar

论文摘要

我们检查了Gaia天文标准揭示的北美/鹈鹕星云的年轻恒星物体(YSO)的聚类和运动学,与分子气体的结构和运动有关,如分子线图所示。盖亚(Gaia)的视差和正确的动作使我们能够显着完善先前发布的YSO列表,表明许多先前认为形成分布式人群的对象被证明是非成员。将成员细分为至少6个时空基团,每个组都与其自身的分子云成分或组件相关。三个组正在扩展,速度梯度为0.3-0.5 km/s/pc,距组中心的最大速度最高约为8 km/s。与该区域相关的两个已知的O-Type恒星,2MASS J20555125+4352246和HD 199579,迅速逃脱了这些组之一,遵循与低质量恒星相同的位置 - 速度关系。我们计算出,从分子气体的块状分布中驱动气体和潮汐力的组合可以赋予组内观察到的速度梯度。但是,在全球范围内,两组的相对运动似乎没有发散或收敛。整个系统的速度分散与由于复合物的重力崩溃而获得的动能一致。大多数恒星人口的年龄类似于出生云的自由落体时间尺度。因此,我们认为湍流分子云几乎自由落体倒塌是该复合物中恒星形成的最可能场景。

We examine the clustering and kinematics of young stellar objects (YSOs) in the North America/Pelican Nebulae, as revealed by Gaia astrometry, in relation to the structure and motions of the molecular gas, as indicated in molecular line maps. The Gaia parallaxes and proper motions allow us to significantly refine previously published lists of YSOs, demonstrating that many of the objects previously thought to form a distributed population turn out to be non-members. The members are subdivided into at least 6 spatio-kinematic groups, each of which is associated with its own molecular cloud component or components. Three of the groups are expanding, with velocity gradients of 0.3-0.5 km/s/pc, up to maximum velocities of ~8 km/s away from the groups' centers. The two known O-type stars associated with the region, 2MASS J20555125+4352246 and HD 199579, are rapidly escaping one of these groups, following the same position-velocity relation as the low-mass stars. We calculate that a combination of gas expulsion and tidal forces from the clumpy distribution of molecular gas could impart the observed velocity gradients within the groups. However, on a global scale, the relative motions of the groups do not appear either divergent or convergent. The velocity dispersion of the whole system is consistent with the kinetic energy gained due to gravitational collapse of the complex. Most of the stellar population has ages similar to the free-fall timescales for the natal clouds. Thus, we suggest the nearly free-fall collapse of a turbulent molecular cloud as the most likely scenario for star formation in this complex.

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