A serendipitous survey for variability amongst the massive stellar population of Westerlund 1
A serendipitous survey for variability amongst the massive stellar population of Westerlund 1
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对 Westerlund 1 大量恒星群体中变异性的一次偶然调查
DOI：
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发表时间：
2010
期刊：
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通讯作者：
I. Negueruela
中科院分区：
文献类型：
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作者：
J. Clark;B. Ritchie;B. Ritchie;I. Negueruela
目标。已知大质量恒星在很宽的时间尺度上表现出显著的光谱和光度变化。然而，驱动这种行为的物理机制仍然知之甚少。Westerlund 1提出了一个理想的实验室，研究这些过程中丰富的，同时代的人口后主序星，我们提出了一个寻路研究，目的是在表征他们的变化。方法.为了做到这一点，我们利用了在过去十年的深入研究中为Wd 1积累的大量光谱和光度数据，并补充了可追溯到20世纪60年代初的稀疏历史观测。结果尽管这个数据集的异质性，我们能够识别光谱和光度的变化之间的每一类的演化大质量星星存在于Wd 1。光谱的变化归因于风作为phericity和光球脉动之间存在的热和冷的超巨星和前者，也与沃尔夫Rayets。由于数据的限制，我们无法确定OB超巨星风结构的物理来源，注意到它存在于单脉动和双星中。与此相反，我们怀疑沃尔夫射线风的不均匀性是由二元相互作用驱动的，相反，至少有一个冷超巨星的脉动。从早在O 9 I到中F Ia +黄超巨星的光谱类型，都发现了恒星的光层脉动-可能依赖于热超巨星中的光度类别。光谱可变的红超巨星（M2-5 Ia）也是潜在的双星，但需要进一步的观测来证实这一假设。鉴于这些发现，因此，令人惊讶的是，除了W 243之外，没有发现亮蓝变星和黄超巨星的特征偏移的证据。光度和进化状态提供了一种诱人的可能性，可以约束驱动不稳定性的物理机制的性质，这些不稳定性约束和定义了恒星演化在HR图的上游。与此相关的是，冷超巨星之间缺乏长期演化，Wd 1内存在高光度的黄超巨星和红超巨星，这可能会对主序后的演化路径产生强烈的限制，后者的结果显然与之相矛盾。
Aims. Massive stars are known to demonstrate significant spectros copic and photometric variability over a wide range of timescales. However the physical mechanisms driving this behaviour remain poorly understood. Westerlund 1 presents an ideal laboratory for studying these processes in a rich, coeval population of post-main sequence stars and we present a pathfinding study aime d at characterising their variability. Methods. To do this we utilised the large body of spectroscopic and photometric data that has accumulated for Wd1 during the past decade of intensive studies, supplemented with the sparser historical observations extending back to the early 1960s. Results. Despite the heterogeneous nature of this dataset, we were able to identify both spectroscopic and photometric variabil ity amongst every class of evolved massive star present within Wd 1. Spectroscopic variability attributable to both wind as phericity and photospheric pulsations was present amongst both the hot and cool hypergiants and the former, also with the Wolf Rayets. Given the limitations imposed by the data, we were unable to determine the physical origin of the wind structure inferred for the OB supergiants, noting that it was present in both single pulsating and binar y stars. In contrast we suspect that the inhomogineities in t he winds of the Wolf Rayets are driven by binary interactions and, conversely, by pulsations in at least one of the cool hypergiants. Pho tospheric pulsations were found for stars ranging from spectral types as early as O9 I through to the mid F Ia + yellow hypergiants - with a possible dependence on the luminosity class amongst the hot supergiants. The spectroscopically variable red supergiants (M2-5 Ia) are also potential pulsators but require further observations to co nfirm this hypothesis. Given these findings it was therefore r ather surprising that, with the exception of W243, no evidence of the characteristic excursions of both luminous blue variables and yellow hypergiants was found. Nevertheless, future determination of the amplitude and periodicity of these pulsations as a function of temperature, luminosity and evolutionary state holds out the tantalising p ossibility of constraining the nature of the physical mecha nisms driving the instabilities that constrain and define stellar evoluti on in the upper reaches of the HR diagram. Relating to this, the lack of secular evolution amongst the cool hypergiants and the presence of both high-luminosity yellow hypergiants and red supergiants within Wd1 potentially place strong constraints on post-main sequence evolutionary pathways, with the latter result apparently contradicting