First Evidence of Circumstellar Disks around Blue Straggler Stars
First Evidence of Circumstellar Disks around Blue Straggler Stars
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DOI：
10.1086/421460
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发表时间：
2004-04
期刊：
影响因子：
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通讯作者：
O. De Marco;T. Lanz;J. Ouellette;D. Zurek;M. Shara
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文献类型：
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作者：
O. De Marco;T. Lanz;J. Ouellette;D. Zurek;M. Shara
我们对在球状星团 M3、NGC 6752 和 NGC 6397 中发现的六颗蓝色散乱星的光学哈勃太空望远镜太空望远镜成像摄谱仪和微弱天体摄谱仪光谱进行了分析。这些恒星是四个球状星团中主序岔道上方约 50 颗蓝色散乱星和恒星的子样本，这些恒星将在即将发表的论文中介绍。除了这里展示的六颗星之外，其他所有星都可以很好地适应非 LTE 模型的氛围。另一方面，六个不适应者拥有的巴尔默跳跃对于他们的帕邢连续体所隐含的有效温度来说太大了。我们发现，只有当我们考虑到电离星周盘对恒星巴尔默光子的额外吸收时，这些恒星的数据才与模型一致。 H I 和 Ca II 的柱密度是根据圆盘的厚度得出的。这是首次在蓝离散星周围检测到星周盘。附着在恒星上的磁锁盘的存在被认为是一种失去这些恒星诞生时碰撞事件所产生的大角动量的机制。我们的研究暗示的圆盘可能不够大，不足以构成这样的角动量汇，但它们可能是曾经较大的圆盘的残余物。
We present an analysis of optical Hubble Space Telescope Space Telescope Imaging Spectrograph and Faint Object Spectrograph spectroscopy of six blue stragglers found in the globular clusters M3, NGC 6752, and NGC 6397. These stars are a subsample of a set of ~50 blue stragglers and stars above the main-sequence turnoff in four globular clusters that will be presented in a forthcoming paper. All but the six stars presented here can be well fitted with non-LTE model atmospheres. The six misfits, on the other hand, possess Balmer jumps that are too large for the effective temperatures implied by their Paschen continua. We find that our data for these stars are consistent with models only if we account for extra absorption of stellar Balmer photons by an ionized circumstellar disk. Column densities of H I and Ca II are derived as are the the disks' thicknesses. This is the first time that a circumstellar disk is detected around blue stragglers. The presence of magnetically locked disks attached to the stars has been suggested as a mechanism to lose the large angular momentum imparted by the collision event at the birth of these stars. The disks implied by our study might not be massive enough to constitute such an angular momentum sink, but they could be the leftovers of once larger disks.