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arXiv 1405.4528astro-ph.SR
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银河系中心弓形激波源的性质

Properties of bow-shock sources at the Galactic center

J. Sanchez-Bermudez, R. Schödel, A. Alberdi, K. Muzic, C. A. Hummel, J. -U. Pott

摘要:

银河系中心(GC)周围有一群神秘的大质量恒星,它们形成于几个Ma前。这些恒星中的一小部分被发现在一个顺时针的投影盘中围绕着超大质量黑洞SgrA*,这表明它们是在SgrA* 周围以前存在的致密盘中形成的。我们专注于扩展的近红外(NIR)源IRS1W,IRS5,IRS10W和IRS21,它们被认为是年轻的大质量恒星,通过与ISM的相互作用形成弓形激波。它们的性质妨碍了对其轨道参数的准确测定。我们的目的是建立他们的性质和运动学,以测试他们是否形成顺时针磁盘的一部分。我们使用自适应光学(AO)和稀疏孔径掩模(SAM)进行近红外多波长成像。介绍了一种在稠密星场中自标定SAM PSF的新方法。通过三维弓形激波模型研究了目标的发射机制、形态和运动学。我们证实了以前的研究结果,IRS21,IRS1W和IRS5是由质量损失的恒星和星际气体之间的相互作用产生的弓形激波。IRS10W的性质仍不清楚。我们的模拟表明,弓激波辐射是由热辐射引起的,而恒星光的散射并不起任何重要作用。IRS 1W似乎是由各向异性恒星风或局部不均匀的ISM密度产生的弓形激波。我们的最佳拟合模型提供了一个估计的本地自行的ISM在NA与公布的模型一致。假设所有源都与SgrA* 有关,通过蒙特卡罗模拟获得它们的轨道平面。我们的轨道分析表明,它们不是任何顺时针圆盘的一部分。因此,我们增加了更多的证据,最近的发现,大部分的大质量恒星显示明显随机的轨道取向。

英文摘要:

There are an enigmatic population of massive stars around the Galactic Center (GC) that were formed some Ma ago. A fraction of these stars has been found to orbit the supermassive black hole, SgrA*, in a projected clockwise disk, which suggests that they were formed in a formerly existing dense disk around SgrA*. We focus on the extended, near-infrared (NIR) sources IRS1W, IRS5, IRS10W, and IRS21 that have been suggested to be young, massive stars that form bow-shocks through their interaction with the ISM. Their nature has impeded accurate determination of their orbital parameters. We aim at establishing their nature and kinematics to test whether they form part of the clockwise disk. We performed NIR multi-wavelength imaging using adaptive optics (AO) and sparse aperture masking (SAM). We introduce a new method for self-calibration of the SAM PSF in dense stellar fields. The emission mechanism, morphology and kinematics of the targets were examined via 3D bow-shock models. We confirm previous findings that IRS21, IRS1W, and IRS5 are bow-shocks created by the interaction between mass-losing stars and the interstellar gas. The nature of IRS10W remains unclear. Our modeling shows that the bow-shock-emission is caused by thermal emission while the scattering of stellar light does not play any significant role. IRS 1W appears to be a bow-shock produced by an anisotropic stellar wind or by locally inhomogeneous ISM density. Our best-fit models provide an estimate of the local proper motion of the ISM in the NA in agreement with the published models. Assuming that all of the sources are tied to SgrA*, their orbital planes were obtained via a Monte-Carlo simulation. Our orbital analysis suggests that they are not part of any of the clockwise disk. We thus add more evidence to recent findings that a large part of the massive stars show apparently random orbital orientations.

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