arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1612.04575astro-ph.SR
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A型恒星会爆发吗?

Do A-type stars flare?

M. G. Pedersen, V. Antoci, H. Korhonen, T. R. White, J. Jessen-Hansen, J. Lehtinen, S. Nikbakhsh, J. Viuho

摘要:

要产生耀斑,恒星必须有足够深的外对流区(F5及以后)、强的大尺度磁场(Ap/Bp型恒星)或强的辐射驱动风(B5及以前)。正常的A型恒星不具备这些,因此不应该耀斑。尽管如此,耀斑之前已经在33颗A型恒星的开普勒光变曲线中被检测到,并被解释为恒星的内在特征。在这里,我们提出了新的和详细的分析,这33颗恒星,实施非常严格的标准,耀斑检测。我们确认存在的耀斑般的功能,在27的33个A型星。对像素数据和周围视场的研究表明,这27个发光物体中有14个有重叠的相邻恒星,5颗恒星在像素数据中显示出明显的污染。我们已经获得了整个样品的2/3的高分辨率光谱,并确认我们的目标确实是A型星。详细的分析显示,19颗恒星中有11颗是光谱双星。此外,与以前的研究相反,我们发现耀斑可以起源于一个较冷的,未解决的同伴。我们注意到H $α$发射在八颗恒星的存在。这种辐射是来自星周还是磁场,目前还不清楚。总之,我们找到了可能的替代解释所观察到的耀斑的33个A型恒星中的至少19个,但没有找到真正令人信服的目标,以支持耀斑的A型恒星的假设。

英文摘要:

For flares to be generated, stars have to have a sufficiently deep outer convection zone (F5 and later), strong large--scale magnetic fields (Ap/Bp-type stars) or strong, radiatively driven winds (B5 and earlier). Normal A-type stars possess none of these and therefore should not flare. Nevertheless, flares have previously been detected in the Kepler lightcurves of 33 A-type stars and interpreted to be intrinsic to the stars. Here we present new and detailed analyses of these 33 stars, imposing very strict criteria for the flare detection. We confirm the presence of flare-like features in 27 of the 33 A-type stars. A study of the pixel data and the surrounding field-of-view (FOV) reveals that 14 of these 27 flaring objects have overlapping neighbouring stars and 5 stars show clear contamination in the pixel data. We have obtained high-resolution spectra for 2/3 of the entire sample and confirm that our targets are indeed A-type stars. Detailed analyses revealed that 11 out of 19 stars with multiple epochs of observations are spectroscopic binaries. Furthermore, and contrary to previous studies, we find that the flares can originate from a cooler, unresolved companion. We note the presence of H$α$ emission in eight stars. Whether this emission is circumstellar or magnetic in origin is unknown. In summary, we find possible alternative explanations for the observed flares for at least 19 of the 33 A-type stars, but find no truly convincing target to support the hypothesis of flaring A-type stars.

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